generated from nerf/texTemplate
I'm scared
This commit is contained in:
parent
0ef95e1735
commit
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20 changed files with 1336 additions and 465 deletions
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in {
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in {
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default = pkgs.stdenvNoCC.mkDerivation {
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default = pkgs.stdenvNoCC.mkDerivation {
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name = "output.pdf";
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name = "output.pdf";
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buildInputs = [latex latexrun pkgs.biber pkgs.inkscape];
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buildInputs = [latex latexrun pkgs.biber pkgs.inkscape pkgs.stix-two];
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src = self;
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src = self;
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buildPhase = ''
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buildPhase = ''
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HOME=.
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HOME=.
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filetypes = ["latex"]
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filetypes = ["latex"]
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roots = [".git", "Main.tex"]
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roots = [".git", "Main.tex"]
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command = "texlab"
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command = "texlab"
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args = ["-vvvv", "--log-file", "/tmp/texlabLog"]
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# args = ["-vvvv", "--log-file", "/tmp/texlabLog"]
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settings_section = "texlab"
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settings_section = "texlab"
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[language.latex.settings.texlab.build]
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[language.latex.settings.texlab.build]
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onSave = true
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onSave = true
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colorscheme solarized-dark
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colorscheme solarized-dark
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set global tabstop 2
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set global tabstop 2
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set global indentwidth 0
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set global indentwidth 0
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eval %sh{kak-lsp --kakoune --session $kak_session -c ${kak-lsp-config} --log /tmp/kak-lspLog -vvvv}
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# eval %sh{kak-lsp --kakoune --session $kak_session -c ${kak-lsp-config} --log /tmp/kak-lspLog -vvvv}
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# eval %sh{kak-lsp --kakoune --session $kak_session -c ${kak-lsp-config}}
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eval %sh{kak-lsp --kakoune --session $kak_session -c ${kak-lsp-config}}
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hook global WinSetOption filetype=(latex) %{
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hook global WinSetOption filetype=(latex) %{
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lsp-enable-window
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vim
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src/Main.tex
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src/Main.tex
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\documentclass[DIV=calc,draft=true]{scrartcl}
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\begin{filecontents*}[overwrite]{\jobname.xmpdata}
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\Title{A uniform equivariant model for cubical type thoery}
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\Author{Dennis Frieberg}
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\Language{en-US}
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\Subject{see title}
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\Keywords{keyword}
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\end{filecontents*}
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\documentclass[DIV=calc,fontsize=12pt,draft=true,parskip]{scrartcl}
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\usepackage[a-2b,mathxmp]{pdfx}[2018/12/22]
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%\usepackage{pdfmanagement-testphase}
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%\DeclareDocumentMetadata{
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% pdfversion=1.7
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%}
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\usepackage{microtype}
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\usepackage{microtype}
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\usepackage{amsthm} %theorems
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\usepackage{amsthm} %theorems
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\usepackage{mathtools} %coloneqq and other stuff
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\usepackage{mathtools} %coloneqq and other stuff
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\usepackage{amssymb}
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\usepackage{amssymb}
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%\usepackage[colon=literal]{unicode-math-luatex} %unicode in mathmode does conflict amssymb maybe sometimes use this line if you want
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%\usepackage[colon=literal]{unicode-math-luatex} %unicode in mathmode does conflict amssymb maybe sometimes use this line if you want
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% that : behaves like \colon
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% that : behaves like \colon
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\usepackage{unicode-math-luatex}
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\usepackage{fontspec} % for changing text fonts (we roll default right now, so no use)
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\usepackage{imakeidx} %make index possible
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\usepackage{unicode-math} %also loads fontspec
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\setmathfont{STIXTwoMath-Regular.otf}
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\setmainfont{STIXTwoText}[Extension=.otf, UprightFont = *-Regular, BoldFont = *-SemiBold, ItalicFont = *-Italic, BoldItalicFont = *-SemiBoldItalic]
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\addtokomafont{disposition}{\rmfamily}
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% \usepackage{imakeidx} %make index possible
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% \makeindex[columns=3, title=Alphabetical Index]
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% \makeindex[columns=3, title=Alphabetical Index]
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\usepackage{graphicx}
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\usepackage{faktor}
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\usepackage{polyglossia}
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\setdefaultlanguage[variant=us]{english}
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\usepackage[obeyDraft]{todonotes}
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\usepackage{subfiles}
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% \usepackage{mathabx}
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\usepackage{pdftexcmds} % pdftex primitves for lualatex
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\usepackage{pdftexcmds} % pdftex primitves for lualatex
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\makeatother
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\DeclareFontFamily{U}{min}{}
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\DeclareFontShape{U}{min}{m}{n}{<-> udmj30}{}
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\newcommand\Yo{\!\text{\usefont{U}{min}{m}{n}\symbol{'207}}\!}
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\newcommand*{\printline}{\number\inputlineno\xspace}
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\renewcommand{\todo}[2][]{\oldtodo[#1]{\printline #2}}
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\addbibresource{resource.bib}
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\theoremstyle{definition}
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\swapnumbers
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\newtheorem{theorem}{Theorem}[subsection]
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\newtheorem{example}[theorem]{Example}
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\newtheorem{proposition}[theorem]{Proposition}
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\newtheorem{observation}[theorem]{Observation}
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\DeclareMathOperator{\Obj}{Obj}
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\begin{document}
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\begin{document}
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\maketitle
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\newpage
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\subfile{Preliminaries/Preliminaries}
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src/Preliminaries/Algebraic_Weak_Factorization_System.tex
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src/Preliminaries/Algebraic_Weak_Factorization_System.tex
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\documentclass[../Main.tex]{subfiles}
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\begin{document}
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\begingroup
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\section{Algebraic Weak Factorization Systems}
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In this section, we will revisit the basic ideas of algebraic weak factorization systems (awfs).
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We won't use them much explicitly through this paper, but we need one major result about them.
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Also, while we don't talk about them explicitly, their ideas permeate through most of the arguments.
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We will only repeat the most basic definitions and ideas, which will be enough to understand
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this document. For a much more complete and in depth discussion, see
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\cites{riehlAlgebraicModelStructures2011}{bourkeAlgebraicWeakFactorisation2016}{bourkeAlgebraicWeakFactorisation2016a}.
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This introduction follows the approach of \cite[Section 2]{riehlAlgebraicModelStructures2011}.
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If the reader is already familiar with this concept, they might safely skip this section.
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We start this section with some observations about regular functorial weak factorization systems (wfs).
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For the remainder of this section we write \({\E : \A^→ → \A^𝟛}\) as the factorization functor of some functorial
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wfs \((\L,\R)\). We are going to write \(\d^0 , \d^2 : \A^𝟛 → A^→\) for the functors induced by \(d_0, d_2 : 𝟚 → 𝟛\).
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\LF and \RF for the endofunctors \(\A^→ → \A^→\) that are given by
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\(\d^2\E\) and \(\d^0\E\), the projection to the left or right factor of the factorization.
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For a given \(f : X → Y\), we call the factoring object \(\E_f\).
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\begin{eqcd*}[column sep =small]
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& \E_f \arrow[rd,"\RF(f)"] & \\
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X \arrow[rr,"f"] \arrow[ru,"\LF(f)"] & & Y
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\end{eqcd*}
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For now, we are interested in witnessing if some map is in the right class (or dually left class). Or in other words,
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attaching some kind of data to a right map from which we could deduce all solutions of the required lifting
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problem. This is indeed possible. Assume that \(f\) is a right map, then a retraction \(r_f\) of \(\LF(f)\) would suffice.
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Assume we had some left map \(f'\) and a lifting problem given by \((g,h)\). We can then factor this with the help of \E.
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\begin{eqcd*}[row sep=huge, column sep=huge]
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X' \arrow[dd,"f'"', bend right] \arrow[d,"\LF(f')"] \arrow[r,"g"] & X \arrow[d,"\LF(f)"] \arrow[dd,"f",bend left=50]\\
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\E_{f'} \arrow[d,"\RF(f')"] \arrow[r, "ϕ_{g,h}"] & \E_f \arrow[d,"\RF(f)"] \arrow[u, "r_f", bend left]\\
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Y' \arrow[r,"h"] \arrow[ur, dashed] & Y
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\end{eqcd*}
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And then compose the solution for the whole lifting problem from the lifting of the problem \((g L(f), h)\) with
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\(r_f\). That this is a solution is guaranteed by \(r_f\) being a retract \(r_f L(f) = \id\). Dually we can
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we automatically get a canonical choice of lifts.
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\begin{eqcd}[row sep=huge, column sep=huge] \label{eq:coalgebraliftsalgebra}
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X' \arrow[dd,"f'"', bend right=50] \arrow[d,"\LF(f')"] \arrow[r,"g"] & X \arrow[d,"\LF(f)"] \arrow[dd,"f",bend left=50]\\
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\E_{f'} \arrow[d,"\RF(f')"'] \arrow[r, "ϕ_{g,h}"] & \E_f \arrow[d,"\RF(f)"'] \arrow[u, "r_f", bend left]\\
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Y' \arrow[r,"h"] \arrow[u, bend right, "s_{f'}"'] & Y
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\end{eqcd}
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Namely for a lifting problem \((g,h)\) the map \(r_f ϕ_{g,h} s_{f'}\), and if we make \(r_f\) and \(s_{f'}\) part of the
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data of a right- (left-) map the chosen lifts are even functorial.
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The next question one might rightfully ask, if we can always find such a witness. And the answer is happily yes.
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We just need to make up the right lifting problem.
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\begin{equation*}
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\begin{tikzcd}[ampersand replacement=\&,column sep = large, row sep = large]
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||||||
|
X' \arrow[d,"f'"'] \arrow[r,"\LF(f')"]\& \E_{f'} \arrow[d, "\RF(f')"] \& \& X \arrow[r,equal] \arrow[d,"\LF(f)"'] \& X \arrow[d,"f"] \\
|
||||||
|
Y' \arrow[r,equal] \arrow[ru, "s_{f'}", dashed] \& Y' \& \& \E_f \arrow[r,"\RF(f)"] \arrow[ru,dashed,"r_f"] \& Y
|
||||||
|
\end{tikzcd}
|
||||||
|
\end{equation*}
|
||||||
|
We can also repack this information in a slightly different way, \(f\) is a right map exactly if \(f\) is a retract of
|
||||||
|
\(\R(f)\) in \(\faktor{\A}{Y}\). And \(f'\) is a left map precisely if \(f'\) is a retract of \(\LF(f)\) in \(\faktor{X'}{\A}\).
|
||||||
|
\begin{eqcd*}
|
||||||
|
X
|
||||||
|
\arrow[d,"f"]
|
||||||
|
\arrow[r, "\LF(f)"]
|
||||||
|
& E_f
|
||||||
|
\arrow[d, "\RF(f)"]
|
||||||
|
\arrow[r, "r_f", dashed]
|
||||||
|
& X
|
||||||
|
\arrow[d, "f"]
|
||||||
|
&
|
||||||
|
& X'
|
||||||
|
\arrow[d,"f'"]
|
||||||
|
\arrow[r, equal]
|
||||||
|
& X'
|
||||||
|
\arrow[r, equal]
|
||||||
|
\arrow[d, "\LF(f)"]
|
||||||
|
& X'
|
||||||
|
\arrow[d, "f'"]
|
||||||
|
\\
|
||||||
|
Y
|
||||||
|
\arrow[r,equal]
|
||||||
|
& Y
|
||||||
|
\arrow[r, equal]
|
||||||
|
& Y
|
||||||
|
&
|
||||||
|
& Y'
|
||||||
|
\arrow[r, "s_{f'}", dashed]
|
||||||
|
& E_{f'}
|
||||||
|
\arrow[r, "\RF(f')"]
|
||||||
|
& Y'
|
||||||
|
\end{eqcd*}
|
||||||
|
If we focus on the diagram at the left-hand side, we can also see it as a morphism \(η_f : f → \RF(f)\) in \(\A^→\), completely dictated
|
||||||
|
by \(\E\) and thus natural in \(f\), and a morphism \(α : \RF(f) → f\), such that \(αη_f = \id\).
|
||||||
|
If we reformulate what we have just observed, we get to the following.
|
||||||
|
\begin{observation}
|
||||||
|
In a functorial wfs \((\L,\R)\) on \A, \(\LF : \A → \A \) is a copointed endofunctor and \RF is pointed endofunctor,
|
||||||
|
where the counit \(ε : \LF → \Id\) is given by the squares \(ε_f ≔
|
||||||
|
\begin{tikzcd}
|
||||||
|
\cdot \arrow[d,"\LF(f)"] \arrow[r,equal] & \cdot \arrow[d,"f"]\\
|
||||||
|
\cdot \arrow[r,"\RF(f)"] & \cdot
|
||||||
|
\end{tikzcd}
|
||||||
|
\)
|
||||||
|
and the unit \(η : \Id → \RF\) by \( η_f ≔
|
||||||
|
\begin{tikzcd}
|
||||||
|
\cdot \arrow[d,"f"] \arrow[r,"\LF(f)"'] & \cdot \arrow[d,"\RF(f)"'] \\
|
||||||
|
\cdot \arrow[r,equal] & \cdot
|
||||||
|
\end{tikzcd}
|
||||||
|
\). \L is precisely the class of \LF-coalgebras and \R the class of \RF-algebras.
|
||||||
|
\end{observation}%
|
||||||
|
One should think of these (co)algebras as morphism with a choice of liftings.
|
||||||
|
At this point, we might try to get rid of the wfs \((\L,\R)\) as input data and might to try to recover it from the
|
||||||
|
factorization functor. And that works described by the methods above, but only if we know that this factorization
|
||||||
|
functor comes from a wfs. If we just start with an arbitrary factorization functor, we still get that all
|
||||||
|
\RF-algebras right lift to all \LF-algebras and vice versa,
|
||||||
|
but in general \(\RF(f)\) will not be a \RF-algebra.
|
||||||
|
One way to solve this problem is by adding a second natural transformation \(\RF\RF → \RF\), such that
|
||||||
|
the neccessary data commute, making \RF a monad (and dually \LF a comand).
|
||||||
|
|
||||||
|
\begin{definition}\label{def:awfs:awfs}
|
||||||
|
An \emph{algebraic weak factorization system (awfs)} is given by a functor \(\E : \A^→ → \A^𝟛\) and two natural transformations
|
||||||
|
\(δ\) and \(μ\). We write \((\LF,ε)\) where \(\LF ≔ \d^2\E\) and \((\RF,η)\) where \(\RF ≔ \d^0\E\) for the two induced
|
||||||
|
pointed endofunctors \(\A^→ → \A^→\). We require that \((\LF,ε,δ)\) is a comonad and \((\RF,η,μ)\) is a monad.\footnote{%
|
||||||
|
Most modern definitions require additionaly that a certain induced natural transformation to be a distributive law of the comonad
|
||||||
|
over the monad. While we recognise its technical important,but we feel that it is distracting from our goal to get the
|
||||||
|
general ideas across.}
|
||||||
|
\end{definition} \todo{this definition is terrible but i can't get it into nice sounding sentence}
|
||||||
|
\begin{notation}
|
||||||
|
If the rest of the data is clear from context we will only specify the comonad and monad and say \((\LF,\RF)\) to be an
|
||||||
|
algebraic weak factorization system.
|
||||||
|
\end{notation}
|
||||||
|
|
||||||
|
\begin{remark}\label{rem:awfs:retractClosure}
|
||||||
|
Neither the \LF-coalgebras nor the \RF-algebras are in general closed under retracts, if we think of them
|
||||||
|
as comonad and monad. But we get a full wfs by taking the \LF-coalgebras and \RF-algebras if we only
|
||||||
|
regard them as the pointed endofunctor, which is the same as the retract closure of the algebras in the (co)monad sense.
|
||||||
|
\end{remark}
|
||||||
|
|
||||||
|
In light of this remark we can pass back from any awfs to a wfs. We can think of this operation as forgetting the choice
|
||||||
|
of liftings.
|
||||||
|
\begin{definition}
|
||||||
|
Let \(\LF,\RF\) be an awfs. We will call \((\L,\R)\) the underlying wfs of \((\LF,\RF)\), where \L is the class
|
||||||
|
of \LF-coalgebras (as a pointed endofunctor) and \R is the class of \RF-algebras (as a pointed endofunctor).
|
||||||
|
\end{definition}
|
||||||
|
\begin{remark}
|
||||||
|
Dropping the algebraic structure is not a lossless operation. Even though the (co)pointed endofunctors and (co)algebras
|
||||||
|
with respect to those endofunctors
|
||||||
|
can be recovered (with enough classical principles), the unit and counit might not have been unique. And thus also
|
||||||
|
not the category of (co)algebras regarding the (co)monad structure.
|
||||||
|
\end{remark}
|
||||||
|
|
||||||
|
We will end this discussion with a few definitions and a theorem that we will later need. While we think the reader
|
||||||
|
is now well prepared to understand the statements and their usefulness, we are aware that we didn't cover
|
||||||
|
enough theory to understand its inner workings.\todo{is this wording ok? should I not do it? I don't want to scare
|
||||||
|
people}
|
||||||
|
|
||||||
|
\begin{definition}\label{def:awfs:rightMaps}
|
||||||
|
Let \J be category and \(J : \J → \A^→\) be a functor. Then an object of the category \(J^⧄\) of \emph{right \(J\)-maps}
|
||||||
|
is a pair \((f,j)\) with \(f\) in
|
||||||
|
\(\A^→\) and \(j\) a function that assigns for every object \(i\) in \J, and for every
|
||||||
|
lifting problem
|
||||||
|
\begin{equation*}
|
||||||
|
\begin{tikzcd}[column sep=huge,row sep=huge]
|
||||||
|
L \arrow[r,"α"] \arrow[d, "J(i)"'] & X \arrow[d,"f"] \\
|
||||||
|
M \arrow[r,"β"] \arrow[ur, dashed,"{j(i,α,β)}"] & Y
|
||||||
|
\end{tikzcd}
|
||||||
|
\end{equation*}
|
||||||
|
a specified lift \(j(i,α,β)\), such that for every \((a,b) : k → i\) in \J, the diagram
|
||||||
|
\begin{equation*}
|
||||||
|
\begin{tikzcd}[column sep=huge, row sep = huge]
|
||||||
|
L' \arrow[r,"a"] \arrow[d,"J(k)"'] & L \arrow[r,"α"] \arrow[d,"J(i)", near end] & X \arrow[d,"f"] \\
|
||||||
|
M' \arrow[urr, dashed, near start, "{j(i,αa,βb)}"] \arrow[r,"b"] & M \arrow[ur, dashed, "{j(i,α,β)}"'] \arrow[r,"β"] & Y
|
||||||
|
\end{tikzcd}
|
||||||
|
\end{equation*}
|
||||||
|
commutes. And morphisms are morphisms in \(\A^→\) that preserve these liftings.
|
||||||
|
\end{definition}
|
||||||
|
\begin{remark}
|
||||||
|
This is even a functor \((−)^⧄ : \faktor{\mathbf{Cat}}{\A^→} → \left(\faktor{\mathbf{Cat}}{\A^→}\right)^\op\)
|
||||||
|
\end{remark}
|
||||||
|
\begin{remark}
|
||||||
|
There is an adjoint notion of left lifting.
|
||||||
|
\end{remark}
|
||||||
|
\begin{remark}
|
||||||
|
This is a strong generalization from the usual case, where one talks about sets (or classes) that lift against each other.
|
||||||
|
If one believes in strong enough choice principles, then the usual case is equivalent
|
||||||
|
to \(\J\) beeing a discrete category and \(J\) some monic functor.
|
||||||
|
\end{remark}
|
||||||
|
We will now turn to a theorem that will provide us with awfs that are right lifting to some functor \(J\).
|
||||||
|
It is (for obvious reasons) known as Garners small object argument.
|
||||||
|
|
||||||
|
\begin{theorem}[{Garner \cites{garnerUnderstandingSmallObject2009}[Theorem 2.28, Lemma 2.30]{riehlAlgebraicModelStructures2011}}]\label{awfs:smallObject}
|
||||||
|
Let \(\A\) be a cocomplete category satisfying either of the following conditions.
|
||||||
|
\begin{itemize}
|
||||||
|
\item[(\(*\))] Every \(X ∈ \A\) is \(α_X\)-presentable for some regular cardinal \(α_X\).
|
||||||
|
\item[(\dagger)] Every \(X ∈ \A\) is \(α_X\)-bounded with respect to some proper, well-copowered
|
||||||
|
orthogonal factorization system on \(\A\), for some regular cardinal \(α_X\).
|
||||||
|
\end{itemize}
|
||||||
|
Let \( J : \mathcal{J} → \A^→\) be a category over \(\A^→\), with \(\mathcal{J}\) small. Then the free awfs on \(\mathcal{J}\) exists,
|
||||||
|
its category of \RF algebras is isomorphic to \(J^⧄\), and the category of \RF-algebras is retract closed.
|
||||||
|
\end{theorem}
|
||||||
|
|
||||||
|
\endgroup
|
||||||
|
\end{document}
|
|
@ -1,19 +1,19 @@
|
||||||
\documentclass[../Main.tex]{subfiles}
|
\documentclass[../Main.tex]{subfiles}
|
||||||
\begin{document}
|
\begin{document}
|
||||||
\section{Cubical Type Theory}
|
\section{Cubical Type Theory}
|
||||||
This section is mainly to give the reader which is not aquainted with cubical type theory
|
This section is mainly to give the reader which is not acquainted with cubical type theory
|
||||||
some guidance and intuition. The reader that already is well-versed in this regard might
|
some guidance and intuition. The reader that already is well-versed in this regard might
|
||||||
skip this section. We still expect the reader to be familiar with some form of univalent
|
skip this section. We still expect the reader to be familiar with some form of univalent
|
||||||
type theory. For a more technical complete presentation we point at \cite{ABCHFL} and \cite{cavalloUnifyingCubicalModels2020}.
|
type theory. For a more technical complete presentation we point at \cite{ABCHFL} and \cite{cavalloUnifyingCubicalModels2020}.
|
||||||
We think about this in terms of categorical semantics, so we expect the reader to have
|
We think about this in terms of categorical semantics, so we expect the reader to have
|
||||||
basic idea about this. For the basic ideas there is the quite old \cite{jacobsCategoricalLogicType1999}. % TODO find categorical semantics references
|
basic idea about this. For the basic ideas there is the quite old \cite{jacobsCategoricalLogicType1999}. % TODO find categorical semantics references
|
||||||
We also recall some translation between intuition and technical treatments of types those elements and similiar things.
|
We also recall some translation between intuition and technical treatments of types those elements and similar things.
|
||||||
We also want to mention that cubical type theory isn't one type theory, but a zoo of related variances of the same idea.
|
We also want to mention that cubical type theory isn't one type theory, but a zoo of related variances of the same idea.
|
||||||
Usually there is already a model in mind, and we allow our type theory to talk about some features of those.
|
Usually there is already a model in mind, and we allow our type theory to talk about some features of those.
|
||||||
We will briefly talk about this in this section for a more technical treatment take a look at \cite{cavalloUnifyingCubicalModels2020}
|
We will briefly talk about this in this section for a more technical treatment take a look at \cite{cavalloUnifyingCubicalModels2020}
|
||||||
Our presentation follows \cite{ABCHFL}. We state formation rules and describe the intended interpretation and leave
|
Our presentation follows \cite{ABCHFL}. We state formation rules and describe the intended interpretation and leave
|
||||||
out the syntactial rules that captures the behaviour that the interpretation captures, as we think that would
|
out the syntactical rules that captures the behavior that the interpretation captures, as we think that would
|
||||||
not add to further intuition. For the cartesian case these can be found in \cite{ABCHFL} and for the deMorgan case in \cite{CCHM}.
|
not add to further intuition. For the Cartesian case these can be found in \cite{ABCHFL} and for the deMorgan case in \cite{CCHM}.
|
||||||
|
|
||||||
|
|
||||||
\subsection{types and universes}
|
\subsection{types and universes}
|
||||||
|
@ -30,13 +30,13 @@ a pullback.
|
||||||
\end{tikzcd}
|
\end{tikzcd}
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
Of course this means that there have to exist the right amount of morphisms
|
Of course this means that there have to exist the right amount of morphisms
|
||||||
from \(Γ → U\), but this is the property that makes our univese a universe.
|
from \(Γ → U\), but this is the property that makes our universe a universe.
|
||||||
Of course this translation can't be expected to be one to one as pullbacks
|
Of course this translation can't be expected to be one to one as pullbacks
|
||||||
are only defined up to isomorphism. One way to deal with this to make a
|
are only defined up to isomorphism. One way to deal with this to make a
|
||||||
choice of pullbacks (calling these display maps) and require that every small fibrant map is isomorph
|
choice of pullbacks (calling these display maps) and require that every small fibrant map is isomorphic
|
||||||
to one of those display maps. This has further problems though. For example is
|
to one of those display maps. This has further problems though. For example is
|
||||||
substitution functorial on the nose, but if we were to go for display maps this
|
substitution functorial on the nose, but if we were to go for display maps this
|
||||||
correpsonds to building another pullback along a map between contexts. So we
|
corresponds to building another pullback along a map between contexts. So we
|
||||||
would need to make our choice of display maps that these choice of pullbacks
|
would need to make our choice of display maps that these choice of pullbacks
|
||||||
gets functorial on the nose. On the other hand working with maps into \(U\)
|
gets functorial on the nose. On the other hand working with maps into \(U\)
|
||||||
has technical benefits. Substitution becomes precomposition, which
|
has technical benefits. Substitution becomes precomposition, which
|
||||||
|
@ -71,7 +71,7 @@ HoTT, cubical type theory is allowed to talk rather directly about liftings of t
|
||||||
|
|
||||||
\subsubsection{interval, dimensions and cubes}
|
\subsubsection{interval, dimensions and cubes}
|
||||||
Cubical type theory has a rather direct way talking about paths. We allow the type theory to talk about the
|
Cubical type theory has a rather direct way talking about paths. We allow the type theory to talk about the
|
||||||
underlying inteval object. We will use the symbol \(\I\) here. This might be a bit unintuitive because
|
underlying interval object. We will use the symbol \(\I\) here. This might be a bit unintuitive because
|
||||||
these are not necessarily Kan. To not get tangled up in this problem we split our context in two. The first half only containing
|
these are not necessarily Kan. To not get tangled up in this problem we split our context in two. The first half only containing
|
||||||
variables of the interval and later half types as we are used to. Or in other words every context has the form
|
variables of the interval and later half types as we are used to. Or in other words every context has the form
|
||||||
\(Φ;Γ\), where \(Φ\) has the form \(i:\I,j:\I,\dots\), and \(Γ\) is allowed to depend on \(Φ\). We often
|
\(Φ;Γ\), where \(Φ\) has the form \(i:\I,j:\I,\dots\), and \(Γ\) is allowed to depend on \(Φ\). We often
|
||||||
|
@ -86,7 +86,7 @@ where \(Γ\) is empty and we have a closed type \(\cdot ⊢ A\). Then a term
|
||||||
Φ \arrow[r] \arrow[u,dashed,"a", bend left] & * \arrow[r,"A"] & U
|
Φ \arrow[r] \arrow[u,dashed,"a", bend left] & * \arrow[r,"A"] & U
|
||||||
\end{tikzcd}
|
\end{tikzcd}
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
and thus also to a map \(Φ → A\). As \(Φ\) is some representable cube it is isomomorhpic to some \(\Yo c\)
|
and thus also to a map \(Φ → A\). As \(Φ\) is some representable cube it is isomorphic to some \(\Yo c\)
|
||||||
and so this map corresponds by yoneda to an element of \(A(c)\).
|
and so this map corresponds by yoneda to an element of \(A(c)\).
|
||||||
In other words we might think about the elements of \(Φ\) as intervals (with start- and endpoint) in different
|
In other words we might think about the elements of \(Φ\) as intervals (with start- and endpoint) in different
|
||||||
directions.
|
directions.
|
||||||
|
@ -110,14 +110,14 @@ and the following rules
|
||||||
\]
|
\]
|
||||||
|
|
||||||
\subsubsection{cofibrations}
|
\subsubsection{cofibrations}
|
||||||
Models of cubical type thoery are usually cofibrantly generated, and these generating maps have representable
|
Models of cubical type theory are usually cofibrantly generated, and these generating maps have representable
|
||||||
codomain. This is done by restricting our first context half by some form of dimension formulas. So our context gets
|
codomain. This is done by restricting our first context half by some form of dimension formulas. So our context gets
|
||||||
a third part \(Φ;ϕ;Γ\). The exact details depend on the model in question. Following the presentation in
|
a third part \(Φ;ϕ;Γ\). The exact details depend on the model in question. Following the presentation in
|
||||||
in \cite{ABCHFL} we introduce an additional kind of judgements, of the form
|
in \cite{ABCHFL} we introduce an additional kind of judgments, of the form
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
Φ ⊢ α \cofib \quad \textrm{and} \quad Φ ⊢ ϕ \formula
|
Φ ⊢ α \cofib \quad \textrm{and} \quad Φ ⊢ ϕ \formula
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
Our \(ϕ\) will constist of a list of such \(α\), and we think of this as one formula by conjunction of this list.
|
Our \(ϕ\) will consist of a list of such \(α\), and we think of this as one formula by conjunction of this list.
|
||||||
This is expressed by the following rules
|
This is expressed by the following rules
|
||||||
%
|
%
|
||||||
%TODO alignment
|
%TODO alignment
|
||||||
|
@ -144,14 +144,14 @@ get syntactically represented by the following rule.
|
||||||
\end{prooftree}
|
\end{prooftree}
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
Our interpretation will naturally get to be objects in \(\mathbf{Sub}(Φ)\).
|
Our interpretation will naturally get to be objects in \(\mathbf{Sub}(Φ)\).
|
||||||
For exmaple \(Φ ⊢ r = 1\), means that \(r ∈ Φ\) and we can write \(Φ\) as \(Ψ,r:\I\) and the judgment gets
|
For example \(Φ ⊢ r = 1\), means that \(r ∈ Φ\) and we can write \(Φ\) as \(Ψ,r:\I\) and the judgment gets
|
||||||
interpreted as the face inclusion \(⟨\id,1/r⟩:Ψ → Φ\). If we have \(Φ ⊢ r = r'\), we can write \(Φ\) as
|
interpreted as the face inclusion \(⟨\id,1/r⟩:Ψ → Φ\). If we have \(Φ ⊢ r = r'\), we can write \(Φ\) as
|
||||||
\(Ψ,r':\I,r:\I\) and our interpretation becomes the diagonal \(⟨\id,r'/r⟩\). \(Φ⊢ r = r\)
|
\(Ψ,r':\I,r:\I\) and our interpretation becomes the diagonal \(⟨\id,r'/r⟩\). \(Φ⊢ r = r\)
|
||||||
as the identity and \(Φ⊢0=1\) as the inclusion of the empty subobject. Cubical variants disagree which
|
as the identity and \(Φ⊢0=1\) as the inclusion of the empty subobject. Cubical variants disagree which
|
||||||
face inclusions should be allowed. The \cite{CCHM} model does not include the diagonal case, while in
|
face inclusions should be allowed. The \cite{CCHM} model does not include the diagonal case, while in
|
||||||
the cartesian model \cite{ABCHFL} the inclusion of these are important to get fillings from compositions.
|
the Cartesian model \cite{ABCHFL} the inclusion of these are important to get fillings from compositions.
|
||||||
|
|
||||||
We are also allowed to glue these together. For exmaple we might want the right and the top face of a square.
|
We are also allowed to glue these together. For example we might want the right and the top face of a square.
|
||||||
We can do this using the \(∨\) operation.
|
We can do this using the \(∨\) operation.
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
\begin{prooftree}
|
\begin{prooftree}
|
||||||
|
@ -161,7 +161,7 @@ We can do this using the \(∨\) operation.
|
||||||
\end{prooftree}
|
\end{prooftree}
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
We will interpret as the coproduct in \(\mathbf{Sub}(Φ)\), or spelled out as the pushout of a their pullback.
|
We will interpret as the coproduct in \(\mathbf{Sub}(Φ)\), or spelled out as the pushout of a their pullback.
|
||||||
The geometrical intution might be we glue the two subobjects together,
|
The geometrical intuition might be we glue the two subobjects together,
|
||||||
along their intersection. Or as a diagram
|
along their intersection. Or as a diagram
|
||||||
\begin{equation}
|
\begin{equation}
|
||||||
\begin{tikzcd}
|
\begin{tikzcd}
|
||||||
|
@ -173,7 +173,7 @@ along their intersection. Or as a diagram
|
||||||
where the outer square is a pullback and the inner square is a pushout.
|
where the outer square is a pullback and the inner square is a pushout.
|
||||||
|
|
||||||
We also have a third operation, that will take an important role in the development of
|
We also have a third operation, that will take an important role in the development of
|
||||||
getting a constructive model for univalence. Nameliy \(∀\), like the name suggest
|
getting a constructive model for univalence. Namely \(∀\), like the name suggest
|
||||||
it will get interpreted as the right adjoint of the pullback functor between
|
it will get interpreted as the right adjoint of the pullback functor between
|
||||||
subobject categories. We add the following rule
|
subobject categories. We add the following rule
|
||||||
\begin{equation}
|
\begin{equation}
|
||||||
|
@ -182,7 +182,7 @@ subobject categories. We add the following rule
|
||||||
\infer1{Φ⊢∀i:\I.α \cofib}
|
\infer1{Φ⊢∀i:\I.α \cofib}
|
||||||
\end{prooftree}
|
\end{prooftree}
|
||||||
\end{equation}
|
\end{equation}
|
||||||
Geometrically this might be envisioned by only keeping faces that are defined arcoss the
|
Geometrically this might be envisioned by only keeping faces that are defined across the
|
||||||
entirety of that dimension, and then projecting the dimension away.
|
entirety of that dimension, and then projecting the dimension away.
|
||||||
|
|
||||||
|
|
||||||
|
@ -200,7 +200,7 @@ are maps from the interval we can actually evaluate them.
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
Which you can think of as the paths from \(t\) to \(u\) in \(A\), or as the
|
Which you can think of as the paths from \(t\) to \(u\) in \(A\), or as the
|
||||||
ways \(t\) and \(u\) are identifiable. As we want to think about paths as maps
|
ways \(t\) and \(u\) are identifiable. As we want to think about paths as maps
|
||||||
from the interval, get rules similiar to that of function types.
|
from the interval, get rules similar to that of function types.
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
\begin{prooftree}
|
\begin{prooftree}
|
||||||
\hypo{Φ;ϕ;Γ ⊢A}
|
\hypo{Φ;ϕ;Γ ⊢A}
|
||||||
|
@ -221,44 +221,44 @@ with the usual (\(η\)) and (\(β\)) rules as well as \(p\,0 \equiv t\) and \(p\
|
||||||
\subsubsection{terms of intervals}
|
\subsubsection{terms of intervals}
|
||||||
In general there are more terms of the interval as we allowed in the construction of \(ϕ\) above.
|
In general there are more terms of the interval as we allowed in the construction of \(ϕ\) above.
|
||||||
Which are allowed is usually closely tied to the site of the underlying model. For example in the
|
Which are allowed is usually closely tied to the site of the underlying model. For example in the
|
||||||
\cite{CCHM} model the underlying cite is the lawvere theory of deMorgan algebras, and the terms
|
\cite{CCHM} model the underlying cite is the Lawvere theory of deMorgan algebras, and the terms
|
||||||
of the interval in that are also the terms of a deMorgan algebra. We want to shortly study them
|
of the interval in that are also the terms of a deMorgan algebra. We want to shortly study them
|
||||||
and give some names and intuition to them. We will mostly talk about the \cite{CCHM} model, as the
|
and give some names and intuition to them. We will mostly talk about the \cite{CCHM} model, as the
|
||||||
cartesian case has a lot less morphisms in its site.
|
Cartesian case has a lot less morphisms in its site.
|
||||||
|
|
||||||
Unravelling the definition of a lawvere theory, we get that the site of the \cite{CCHM} consists of
|
Unraveling the definition of a Lawvere theory, we get that the site of the \cite{CCHM} consists of
|
||||||
a skelleton of finite sets and a morphism from \(A\) to \(B\) is a function from \(B\) to the free
|
a skeleton of finite sets and a morphism from \(A\) to \(B\) is a function from \(B\) to the free
|
||||||
deMorgan algebra generated by \(A\). As the yoneda embedding ist fully faithfull this also holds
|
deMorgan algebra generated by \(A\). As the yoneda embedding is fully faithfull this also holds
|
||||||
for the subcategory of representables. A term in some dimensional context \(Φ\) of type \I becomes
|
for the subcategory of representables. A term in some dimensional context \(Φ\) of type \I becomes
|
||||||
a map from \(Φ → \I\), and as this a map from \(\I^n → \I\). These correspond to a term of a deMorgan
|
a map from \(Φ → \I\), and as this a map from \(\I^n → \I\). These correspond to a term of a deMorgan
|
||||||
algebra with \(n\) variables. We will write for this judgements of the form
|
algebra with \(n\) variables. We will write for this judgments of the form
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
Φ ⊢ t : \I
|
Φ ⊢ t : \I
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
We can think of a type in a context with \(n\) dimension variables as an \(n\)-cube
|
We can think of a type in a context with \(n\) dimension variables as an \(n\)-cube
|
||||||
of types. And a term as an \(n\)-cube in the total space of the type, going across the fibres.
|
of types. And a term as an \(n\)-cube in the total space of the type, going across the fibers.
|
||||||
Depending on the map in the site, or equivalently map between the representables, we get terms
|
Depending on the map in the site, or equivalently map between the representables, we get terms
|
||||||
of cubes that we can plug into our types.
|
of cubes that we can plug into our types.
|
||||||
|
|
||||||
For example if we have a line of types, we can look
|
For example if we have a line of types, we can look
|
||||||
at it as a degenerate square of types. These can be done in multiple ways. The obvious one is
|
at it as a degenerate square of types. These can be done in multiple ways. The obvious one is
|
||||||
through weakening. Or syntactically gooing from \(r:\I;; ⊢ A\) to \(r:\I,r':\I;; ⊢ A\). Which gives
|
through weakening. Or syntactically going from \(r:\I;; ⊢ A\) to \(r:\I,r':\I;; ⊢ A\). Which gives
|
||||||
us a square of types that is constant in the direction of \(r'\). In usual topology there are more
|
us a square of types that is constant in the direction of \(r'\). In usual topology there are more
|
||||||
ways to get degenerate a square from a line, for example we might want that the right and the
|
ways to get degenerate a square from a line, for example we might want that the right and the
|
||||||
top face are given line and the left and bottom face is constant. These kind of degeneracies are
|
top face are given line and the left and bottom face is constant. These kind of degeneracies are
|
||||||
usually called connections and exist in some models. In the \cite{CCHM} model this specific
|
usually called connections and exist in some models. In the \cite{CCHM} model this specific
|
||||||
degenracy corresponds to the meet (\(∧\)). Or syntactically more explicit, if we have
|
degeneracy corresponds to the meet (\(∧\)). Or syntactically more explicit, if we have
|
||||||
a line of types \(r:\I⊢A\) we can get a degenarete square of types \(r:\I,r':\I⊢A(r/r∧r')\).
|
a line of types \(r:\I⊢A\) we can get a degenerate square of types \(r:\I,r':\I⊢A(r/r∧r')\).
|
||||||
In point set topology we could think about ths as taking the infimum of \(r\) and \(r'\).
|
In point set topology we could think about this as taking the infimum of \(r\) and \(r'\).
|
||||||
Of course there is also the dual connection, which is also present in \cite{CCHM}. There
|
Of course there is also the dual connection, which is also present in \cite{CCHM}. There
|
||||||
is also a model with only one of the two connections studied in \cite{cavalloRelativeEleganceCartesian2022}
|
is also a model with only one of the two connections studied in \cite{cavalloRelativeEleganceCartesian2022}
|
||||||
These degeneracies allow to reconstruct fillings from compositions. The cartesian model
|
These degeneracies allow to reconstruct fillings from compositions. The Cartesian model
|
||||||
does not have connections, there we will use diagonal cofibrations to get fillings from
|
does not have connections, there we will use diagonal cofibrations to get fillings from
|
||||||
compositions.
|
compositions.
|
||||||
% TODO image of connections.
|
% TODO image of connections.
|
||||||
|
|
||||||
In the \cite{CCHM} model we are also allowed to reverse dimensions. This corresponds
|
In the \cite{CCHM} model we are also allowed to reverse dimensions. This corresponds
|
||||||
to the inversion/negation of the deMorgan algbera. These kind of maps are often called reversals.
|
to the inversion/negation of the deMorgan algebra. These kind of maps are often called reversals.
|
||||||
|
|
||||||
The last map we want to mention here, are diagonals. These correspond syntactically to the diagonals
|
The last map we want to mention here, are diagonals. These correspond syntactically to the diagonals
|
||||||
\(r:\I;; ⊢ (r,r) : \I^2\). The reason to mention them is that the \cite{BCH} model does not feature those
|
\(r:\I;; ⊢ (r,r) : \I^2\). The reason to mention them is that the \cite{BCH} model does not feature those
|
||||||
|
@ -275,7 +275,7 @@ The first thing we need to talk about a filling, is a filling problem.
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
A syntactic representation of the figuratively drawn problem above might be represented by
|
A syntactic representation of the figuratively drawn problem above might be represented by
|
||||||
witnessing the following rule.
|
witnessing the following rule.
|
||||||
\todo{should I also include the judgemental equalities that say that a filling is actually a filling of that problem?}
|
\todo{should I also include the judgmental equalities that say that a filling is actually a filling of that problem?}
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
\begin{prooftree}
|
\begin{prooftree}
|
||||||
\hypo{z: \I ,z':\I ;;Γ ⊢ A \type }
|
\hypo{z: \I ,z':\I ;;Γ ⊢ A \type }
|
||||||
|
@ -288,7 +288,7 @@ Allowing this in its obvious generalization runs directly into problems, as that
|
||||||
liftings against arbitrary cofibrations, and not only trivial ones. To get around this problem
|
liftings against arbitrary cofibrations, and not only trivial ones. To get around this problem
|
||||||
we reformulate our syntactic representation. To do this we split the problem data into two
|
we reformulate our syntactic representation. To do this we split the problem data into two
|
||||||
parts. The first part is the base, that is not allowed to talk about the dimension we want to
|
parts. The first part is the base, that is not allowed to talk about the dimension we want to
|
||||||
fill, but completly defined in all other dimensions, and a part that is allowed to talk about the dimension we want to fill in,
|
fill, but completely defined in all other dimensions, and a part that is allowed to talk about the dimension we want to fill in,
|
||||||
but must be attached to the base and agree with it.
|
but must be attached to the base and agree with it.
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
\begin{prooftree}
|
\begin{prooftree}
|
||||||
|
@ -324,7 +324,7 @@ Or written as the intended commuting diagram
|
||||||
Φ,z:\I \arrow[r] \arrow[ur,"{\mfill(b,t)}", dashed] & Φ,z:\I;;Γ
|
Φ,z:\I \arrow[r] \arrow[ur,"{\mfill(b,t)}", dashed] & Φ,z:\I;;Γ
|
||||||
\end{tikzcd}
|
\end{tikzcd}
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
From a syntactial point of view that rule is not so great, as in the
|
From a syntactical point of view that rule is not so great, as in the
|
||||||
conclusion there is an explicit free variable \(r'\), and it is not
|
conclusion there is an explicit free variable \(r'\), and it is not
|
||||||
at all clear how one would substitute a term for \(r'\) into our filling term.
|
at all clear how one would substitute a term for \(r'\) into our filling term.
|
||||||
The usual way of dealing with this problem is by making \(r'\) a term appearing
|
The usual way of dealing with this problem is by making \(r'\) a term appearing
|
||||||
|
@ -350,9 +350,9 @@ If we translate this back to the world of commutative diagrams we get\footcite[p
|
||||||
Φ \arrow[r,"{(\id,r'/z)}"'] \arrow[rru, dashed,"{\comp_A^{z:r→r}(b,t)}"] & Φ,z:\I \arrow[r] & Φ,z:\I;;Γ
|
Φ \arrow[r,"{(\id,r'/z)}"'] \arrow[rru, dashed,"{\comp_A^{z:r→r}(b,t)}"] & Φ,z:\I \arrow[r] & Φ,z:\I;;Γ
|
||||||
\end{tikzcd}
|
\end{tikzcd}
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
Different variants allow different terms for \(r'\) and \(z\). On one extrem the
|
Different variants allow different terms for \(r'\) and \(z\). On one extreme the
|
||||||
\cite{CCHM} model only allows composition from 0 to 1. Which is in the presence of
|
\cite{CCHM} model only allows composition from 0 to 1. Which is in the presence of
|
||||||
reversals and connections is not really a strong restriction. In the cartesian model
|
reversals and connections is not really a strong restriction. In the Cartesian model
|
||||||
we need to be less restrictive to.
|
we need to be less restrictive to.
|
||||||
|
|
||||||
In general it is not clear that can recover fillings from compositions. So it
|
In general it is not clear that can recover fillings from compositions. So it
|
||||||
|
@ -361,16 +361,16 @@ is not to difficult, and we can define
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
Φ,i:\I;;Γ⊢\mfill_A^z(b,t) ≔ \comp_{A(i/i∧j)}^{a→b}(b,t(i∧j/i)) : A
|
Φ,i:\I;;Γ⊢\mfill_A^z(b,t) ≔ \comp_{A(i/i∧j)}^{a→b}(b,t(i∧j/i)) : A
|
||||||
\end{equation*}\todo{make this technical correct}
|
\end{equation*}\todo{make this technical correct}
|
||||||
\todo{agree on a way to write substitution, why is this not uniform across litrature?}
|
\todo{agree on a way to write substitution, why is this not uniform across literature?}
|
||||||
\todo{make handrawn picture for this}
|
\todo{make hand drawn picture for this}
|
||||||
|
|
||||||
This doesn't work in the cartesian setting though, as we don't have any connections. Here
|
This doesn't work in the Cartesian setting though, as we don't have any connections. Here
|
||||||
we can use the fact that we allowed diagonals in our filling problems. And define
|
we can use the fact that we allowed diagonals in our filling problems. And define
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
Φ,z:\I;;Γ ⊢ \mfill_A^{z:r}(b,t) ≔ \comp_A^{z':r→z}(b,t) : A
|
Φ,z:\I;;Γ ⊢ \mfill_A^{z:r}(b,t) ≔ \comp_A^{z':r→z}(b,t) : A
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
where \(z'\) does not appear in \(Φ\).
|
where \(z'\) does not appear in \(Φ\).
|
||||||
\todo{make handrawn picture for this}
|
\todo{make hand drawn picture for this}
|
||||||
|
|
||||||
\begin{equation}
|
\begin{equation}
|
||||||
\begin{prooftree}
|
\begin{prooftree}
|
||||||
|
|
|
@ -3,14 +3,15 @@
|
||||||
\section{Leibniz Construction}
|
\section{Leibniz Construction}
|
||||||
We will see use a well know construction in homotopy theory, to
|
We will see use a well know construction in homotopy theory, to
|
||||||
elegantly construct a lot of interesting objects, the Leibniz construction.
|
elegantly construct a lot of interesting objects, the Leibniz construction.
|
||||||
This section will recall the definition establish some facts and give some examples.
|
This section will mostly give a definition and some examples to get familiar with this construction.
|
||||||
There are multiple
|
If the reader is already familiar with it, they might skip this section without any problems.
|
||||||
|
|
||||||
We start be giving the definition
|
We start be giving the definition
|
||||||
\begin{definition}[Leibniz Construction]
|
\begin{definition}[Leibniz Construction]
|
||||||
Let \(\A\), \(\B\) and \(\C\) be categories and \(\C\) has finite pushouts. Let \(⊗ : \A × \B → \C \) be a bifunctor.
|
Let \(\A\), \(\B\) and \(\C\) be categories and \(\C\) has finite pushouts. Let \(⊗ : \A × \B → \C \) be a bifunctor.
|
||||||
Then we define \(\hat{⊗} : \arr{\A} × \arr{\B} → \arr{\C}\) to defined as follows. Given \(f : A → A' \) in \(\A\) and
|
Then we define the \emph{Leibniz Construction} \(\hat{⊗} : \arr{\A} × \arr{\B} → \arr{\C}\) to be the functor
|
||||||
\( g : B → B' \) in \(\B\), then \( f \hat{⊗} g \) is defined as in the following diagram.\\
|
that sends \(f : A → A' \) in \(\A\) and
|
||||||
|
\( g : B → B' \) in \(\B\), to \( f \hat{⊗} g \) as defined as in the following diagram.
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
\begin{tikzcd}
|
\begin{tikzcd}
|
||||||
A ⊗ B \arrow[r, "f ⊗ \id"] \arrow[d, "\id ⊗ g"] \arrow[dr, phantom, "\ulcorner", very near end] & A' ⊗ \mathrlap{B} \phantom{A'} \arrow[ddr, bend left, "\id ⊗ g"] \arrow[d] & \\
|
A ⊗ B \arrow[r, "f ⊗ \id"] \arrow[d, "\id ⊗ g"] \arrow[dr, phantom, "\ulcorner", very near end] & A' ⊗ \mathrlap{B} \phantom{A'} \arrow[ddr, bend left, "\id ⊗ g"] \arrow[d] & \\
|
||||||
|
@ -18,34 +19,64 @@ We start be giving the definition
|
||||||
& & A' ⊗ B'
|
& & A' ⊗ B'
|
||||||
\end{tikzcd}
|
\end{tikzcd}
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
\end{definition}
|
If \(⊗\) is the tensor functor of a monoidal category we also call it the \emph{Leibniz product} or \emph{pushout-product}. If \(⊗\) is
|
||||||
When the bifunctor is the cartesian product functor, this construction is also known as the \emph{pushout-product}.
|
the functor application functor we also call it the \emph{Leibniz application}.
|
||||||
Now we will give some examples, some of them instructive and some that will appear later again.
|
|
||||||
|
|
||||||
\begin{example}
|
|
||||||
Let \(\C\) be your favourite category of spaces, \( × \) the cartesian product and \(f = g\) be the
|
|
||||||
inclusion of the point into the start of the interval. Then the pushout-product \(f \hat{×} g \) is the inclusion of
|
|
||||||
two adjacents sides of a square, into that square.
|
|
||||||
\end{example}
|
|
||||||
Or a bit more general
|
|
||||||
\begin{example}\label{Leibniz:Ex:OpenBox}
|
|
||||||
Let \(\C\) be your favourite category of spaces, \( × \) the cartesian poduct. Let \(f\) be the
|
|
||||||
inclusion of one endpoint into the interval. Let \(g : ∂\I^n → \I^n \) be the boundary inclusion into
|
|
||||||
the \(n\)-cube. Then \(f \hat{×} \) is the filling of an \(n\) dimensional open box.
|
|
||||||
\end{example}
|
|
||||||
\begin{example}
|
|
||||||
Let \(\C\) be your favourite category of spaces, and \( @ : \C^{\C} × \C → \C \) defined as
|
|
||||||
\( F @ x ≔ F(x)\) the functor application functor. Let \(\I ⊗ (−)\) be a functorial cylinder and \(i_0\).
|
|
||||||
be one of the inclusions \( i_0 : \Id → \I ⊗ (−) \) and \( ∂X → X \) be the boundery inclusion of \(X\).
|
|
||||||
Then \( i_0 \hat{@} (∂X → X) \) is the filling of a cylinder with one base surface of shape \(X\).
|
|
||||||
\end{example}
|
|
||||||
|
|
||||||
As we will come across this example multiple times it will get some special syntax.
|
|
||||||
|
|
||||||
\begin{definition}
|
|
||||||
|
|
||||||
\end{definition}
|
\end{definition}
|
||||||
|
|
||||||
|
The following examples are true for any category of nice spaces, we will state them for simplicial sets as the reader is probably
|
||||||
|
familiar with them.
|
||||||
|
|
||||||
|
\begin{example}\label{ex:leib:prism}
|
||||||
|
Let \(δ_k : * → Δ^1\) for \(k ∈ {0,1}\) be one of the endpoint inclusions into the interval and \(i : \∂ Δ^n → Δ^n\) the boundary
|
||||||
|
inclusion of the \(n\)-simplex, then \(δ_k \hat{×} i\) is the inclusion of a prism without its interior and one cap, into the prism.
|
||||||
|
\end{example}
|
||||||
|
This gives us a description of a possible set of generating trivial cofibrations. This will be an ongoing theme. For cubical sets we
|
||||||
|
will define trivial cofibrations in this fashion. We can even observe something stronger. If we would replace the boundary inclusion
|
||||||
|
of the \(n\)-simplex with the boundary inclusion of an arbitrary space \(X\). We get the inclusion of the cylinder object of \(X\)
|
||||||
|
without a cap and its interior into the cylinder.
|
||||||
|
\begin{figure}
|
||||||
|
\missingfigure{cylinder inclusion as pushout product}
|
||||||
|
\caption{cylinder inclusion as Leibniz product}
|
||||||
|
\end{figure}
|
||||||
|
|
||||||
|
\begin{observation}
|
||||||
|
If \(f\) and \(g\) are cofibrations then \(f \hat{×} g\) is too. If one of them is a trivial cofibration then so is \(f \hat{×} g\).
|
||||||
|
\end{observation}
|
||||||
|
This has far reaching consequences, and one can define a monoidal model category where this are one of the axioms
|
||||||
|
for the tensor functor. For more
|
||||||
|
detail see \cite{hoveyModelCategories2007}. We are not going to need much of this theory explicitly. But it is worthy to note
|
||||||
|
that all examples of model categories that we are going to encouter are of this form.
|
||||||
|
|
||||||
|
We will also encouter the basically same construction as \cref{ex:leib:prism} in another way. We can also get the Cylinder object
|
||||||
|
functorialy in \Δ, such that the cap inclusions are natural transformations.
|
||||||
|
We can also get the inclusion the Leibniz product produces in a natural manner via the Leibniz application.
|
||||||
|
|
||||||
|
\begin{example}\label{ex:leib:functorialCylinder}
|
||||||
|
Let \( @ : \C^{\C} × \C → \C \) defined as
|
||||||
|
\( F @ x ≔ F(x)\) the functor application functor. Let \(\I × (−)\) be the functor that sends \(X\) to its cylinder object (also known as the
|
||||||
|
product with the interval).
|
||||||
|
Let be one of the inclusions \( δ_k : \Id → \I ⊗ (−) \), the natural transformation that embeds the space in one of the cylinder caps.
|
||||||
|
Let \( \∂ X → X \) be the boundery inclusion of \(X\).
|
||||||
|
Then \( δ_k \hat{@} (∂X → X) \) is the filling of a cylinder with one base surface of shape \(X\).
|
||||||
|
\end{example}
|
||||||
|
This kind of construction will later play an important role in the construction of our desired model categories.
|
||||||
|
|
||||||
|
We will also encouter another form of Leibniz application, which has at first glance not to do alot with homotopy. On
|
||||||
|
the other hand one might read this as, getting the component of an natural transformation is some sort of a homotopic construction.
|
||||||
|
\begin{lemma}
|
||||||
|
Let \(F,G : A → B \) and \(η : F ⇒ G\) be a natural transformation, and \A has in initial object \(∅\). Let
|
||||||
|
\(F\) and \(G\) preserve the initial object.
|
||||||
|
We write \(∅ → X\) for the unique map with the same type. Then we get \(η \at (∅ → X) = η_X\).
|
||||||
|
\end{lemma}
|
||||||
|
\begin{proof}\todo{this is contravariant and I'm too tired}
|
||||||
|
We will draw the diagram from the definiton
|
||||||
|
\begin{eqcd*}
|
||||||
|
F (∅) \arrow[r, "F(∅ → X)"] \arrow[d, "η_∅"] \arrow[dr, phantom, "\ulcorner", very near end] & F(X) \arrow[ddr, bend left, "η_X"] \arrow[d] & \\
|
||||||
|
G(∅) \arrow[drr, bend right, "G(∅ → X)"] \arrow[r] & G(∅) ∐\limits_{F(∅)} \mathrlap{F(X)} \phantom{G(∅)} \arrow[dr, dashed ,"f \hat{⊗} g"] & \\
|
||||||
|
& & G(X)
|
||||||
|
\end{eqcd*}
|
||||||
|
If we substitude \(F(\emptyset)\) and \(G(∅)\) with \(∅\) the claim directly follows.
|
||||||
|
\end{proof}
|
||||||
% TODO Left adjoint
|
% TODO Left adjoint
|
||||||
|
|
||||||
\end{document}
|
\end{document}
|
||||||
|
|
|
@ -1,18 +1,18 @@
|
||||||
\documentclass[../Main.tex]{subfiles}
|
\documentclass[../Main.tex]{subfiles}
|
||||||
\begin{document}
|
\begin{document}
|
||||||
|
|
||||||
\section{Model structure}\label{modelStructure}
|
\section{Model structure}\label{modelStructure}
|
||||||
|
|
||||||
% TODO restructure lifting with respect to category
|
% TODO restructure lifting with respect to category
|
||||||
% awfs
|
% awfs
|
||||||
% Then cubical sets
|
% Then cubical sets
|
||||||
|
|
||||||
|
\subsection{Equivariant Cartesian Cubes}
|
||||||
\subsection{Cartesian Cubes}
|
|
||||||
We now presenting our, main star, the equivariant model structure on cubical sets.
|
We now presenting our, main star, the equivariant model structure on cubical sets.
|
||||||
We will give a description of the two involved factorization systems and then follow
|
We will give a description of the two involved factorization systems and then follow
|
||||||
an argument from \cite{cavalloRelativeEleganceCartesian2022}, to show that it is indeed
|
an argument from \cite{cavalloRelativeEleganceCartesian2022}, to show that it is indeed
|
||||||
a model structure. The modelstructure as well as the presentation is taken from
|
a model structure. The modelstructure as well as the presentation is taken from
|
||||||
\cite{mathematicalsciencesresearchinstitutemsriEquivariantUniformKan2020}. This
|
\cite{riehlVid}. This
|
||||||
equivariant model structure is also know as the ACCRS model structure.
|
equivariant model structure is also know as the ACCRS model structure.
|
||||||
|
|
||||||
% reference for uniform fibrations CCHM and
|
% reference for uniform fibrations CCHM and
|
||||||
|
@ -24,120 +24,98 @@ of the point a trivial cofibration. This is archived by forcing an extra propert
|
||||||
the fibrations.
|
the fibrations.
|
||||||
|
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
\begin{tikzcd}[column sep=large]
|
\begin{tikzcd}[column sep=large, row sep=large]
|
||||||
* \arrow[r,"\id"] \arrow[d,tail,"f"] & * \arrow[d,tail,"σf"'] \arrow[r] & * \arrow[d,tail] \arrow[r,"β"] & X \arrow[d,"f"] \\
|
* \arrow[r,"\id"] \arrow[d,tail,"f"] & * \arrow[d,tail,"σf"'] \arrow[r] & * \arrow[d,tail] \arrow[r,"β"] & X \arrow[d,"f"] \\
|
||||||
\I^2 \arrow[r,"σ"', shift right=0.5ex] \arrow[r,"\id", shift left=0.5ex] \arrow[urrr, dashed, ,near end, "{j(αe,β)}"'] & \I^2 \arrow[urr, dashed, "{j(αeσ,β)}"] \arrow[r, "e"] & Q \arrow[r,"α"] & Y
|
\I^2 \arrow[r,"σ"', shift right=0.7ex] \arrow[r,"\id", shift left=0.7ex] \arrow[urrr, dashed, ,near end, "{j(αe,β)}"'] & \I^2 \arrow[urr, dashed, "{j(αeσ,β)}"] \arrow[r, "e"] & Q \arrow[r,"α"] & Y
|
||||||
\end{tikzcd}
|
\end{tikzcd}
|
||||||
\end{equation*} % Fix twist of suboject
|
\end{equation*} % Fix twist of suboject
|
||||||
|
|
||||||
Here \(e\) is the coequilizer map. The hope would be, that
|
Here \(σ\) is the map that swaps the dimenisons and \(e\) is the coequilizer map. The hope would be, that
|
||||||
the coequilizer, would now present a lift for the right most lifting problem. But in general that
|
the coequilizer, would now present a lift for the right most lifting problem. But in general that
|
||||||
does not hold, the lifts have neither to commute with \(σ\) nor with \(\id\). The path forward
|
does not hold, the lifts have neither to commute with \(σ\) nor with \(\id\). The path forward
|
||||||
will be to restrict the fibrations to have the desired property.
|
will be to restrict the fibrations to have the desired property.
|
||||||
%
|
%
|
||||||
|
|
||||||
\subsubsection{Weak factorization systems}
|
% \subsubsection{Weak factorization systems}
|
||||||
If we force additional properties on our lifting problems, one might rightfully
|
% If we force additional properties on our lifting problems, one might rightfully
|
||||||
ask if these indeed induce a weak factorization system (wfs). It is also unclear if
|
% ask if these indeed induce a weak factorization system (wfs). It is also unclear if
|
||||||
there are induced factorizations at all. The good news is, there is a refined version
|
% there are induced factorizations at all. The good news is, there is a refined version
|
||||||
of the small object argument \ref{smallObject}, that will help us out. This works on
|
% of the small object argument \cref{smallObject}, that will help us out. This works on
|
||||||
the back of algebraic weak factorization systems. We don't need the whole theory and
|
% the back of algebraic weak factorization systems. We don't need the whole theory and
|
||||||
get by with the following definitiont.
|
% get by with the following definitiont.
|
||||||
|
%
|
||||||
\begin{definition}\label{def:rightMaps}
|
% \begin{definition}\label{def:rightMaps}
|
||||||
Let \J be category and \(J : \J → \M^→\) be a functor. Then an object \(f\) in
|
% Let \J be category and \(J : \J → \M^→\) be a functor. Then an object \(f\) in
|
||||||
\(\M^→\) is a \emph{right \(J\)-map} if for every object \(i\) in \J, and for every
|
% \(\M^→\) is a \emph{right \(J\)-map} if for every object \(i\) in \J, and for every
|
||||||
lifting problem
|
% lifting problem
|
||||||
\begin{equation*}
|
% \begin{equation*}
|
||||||
\begin{tikzcd}[column sep=large]
|
% \begin{tikzcd}[column sep=large,row sep=large]
|
||||||
L \arrow[r,"α"] \arrow[d, "Ji"'] & X \arrow[d,"f"] \\
|
% L \arrow[r,"α"] \arrow[d, "Ji"'] & X \arrow[d,"f"] \\
|
||||||
M \arrow[r,"β"] \arrow[ur, dashed,"{j(α,β)}"] & Y
|
% M \arrow[r,"β"] \arrow[ur, dashed,"{j(α,β)}"] & Y
|
||||||
\end{tikzcd}
|
% \end{tikzcd}
|
||||||
\end{equation*}
|
% \end{equation*}
|
||||||
there is a specified lift \(j(α,β)\), such that for every \((a,b) : k → i\) in \J, the diagram
|
% there is a specified lift \(j(α,β)\), such that for every \((a,b) : k → i\) in \J, the diagram
|
||||||
\begin{equation*}
|
% \begin{equation*}
|
||||||
\begin{tikzcd}[column sep=huge]
|
% \begin{tikzcd}[column sep=huge, row sep = large]
|
||||||
L' \arrow[r,"a"] \arrow[d,"Jk"'] & L \arrow[r,"α"] \arrow[d,"Ji"] & X \arrow[d,"f"] \\
|
% L' \arrow[r,"a"] \arrow[d,"Jk"'] & L \arrow[r,"α"] \arrow[d,"Ji"] & X \arrow[d,"f"] \\
|
||||||
M' \arrow[urr, dashed, near start, "{j(αa,βb)}"] \arrow[r,"b"] & M \arrow[ur, dashed, "{j(α,β)}"'] \arrow[r,"β"] & Y
|
% M' \arrow[urr, dashed, near start, "{j(αa,βb)}"] \arrow[r,"b"] & M \arrow[ur, dashed, "{j(α,β)}"'] \arrow[r,"β"] & Y
|
||||||
\end{tikzcd}
|
% \end{tikzcd}
|
||||||
\end{equation*}
|
% \end{equation*}
|
||||||
commutes.
|
% commutes.
|
||||||
\end{definition}
|
% \end{definition}
|
||||||
|
%
|
||||||
\begin{remark}
|
% \begin{remark}
|
||||||
If we start with a set \J and make it into a discret category, then we will get our old definition
|
% If we start with a set \J and make it into a discret category, then we will get our old definition
|
||||||
of right lifting map, with an additional choice function for lifts. Which exists anyway if we
|
% of right lifting map, with an additional choice function for lifts. Which exists anyway if we
|
||||||
are ready to believe in strong enough choice principles.
|
% are ready to believe in strong enough choice principles.
|
||||||
\end{remark}
|
% \end{remark}
|
||||||
|
%
|
||||||
After we defined a class of right maps by those lifting problems, it is not clear that these
|
% After we defined a class of right maps by those lifting problems, it is not clear that these
|
||||||
will yield a wfs.
|
% will yield a wfs.
|
||||||
To get those we invoke a refinment of Quillens small object argument, namely
|
% To get those we invoke a refinment of Quillens small object argument, namely
|
||||||
Garners small object argument \cite{garnerUnderstandingSmallObject2009}. This has the additional benefit of producing
|
% Garners small object argument \cite{garnerUnderstandingSmallObject2009}. This has the additional benefit of producing
|
||||||
algebraic weak factorization systems (awfs). For a quick reference see
|
% algebraic weak factorization systems (awfs). For a quick reference see
|
||||||
\cite{riehlMadetoOrderWeakFactorization2015a}, and for an extensive tour \cite{riehlAlgebraicModelStructures2011}, or
|
% \cite{riehlMadetoOrderWeakFactorization2015a}, and for an extensive tour \cite{riehlAlgebraicModelStructures2011}, or
|
||||||
\cite{bourkeAlgebraicWeakFactorisation2016,bourkeAlgebraicWeakFactorisation2016a}. The main takeaway for
|
% \cite{bourkeAlgebraicWeakFactorisation2016,bourkeAlgebraicWeakFactorisation2016a}. The main takeaway for
|
||||||
us is the following theorem \cite[][Theorem 2.28]{riehlAlgebraicModelStructures2011}
|
% us is the following theorem \cite[][Theorem 2.28]{riehlAlgebraicModelStructures2011}
|
||||||
|
%
|
||||||
\begin{theorem}[Garner]\label{smallObject}
|
% \begin{theorem}[Garner]\label{smallObject}
|
||||||
Let \(\M\) be a cocomplete category satisfying either of the following conditions.
|
% Let \(\M\) be a cocomplete category satisfying either of the following conditions.
|
||||||
\begin{itemize}
|
% \begin{itemize}
|
||||||
\item[(\ast)] Every \(X ∈ \M\) is \(α_X\)-presentable for some regular cardinal \(α_X\).
|
% \item[(\(*\))] Every \(X ∈ \M\) is \(α_X\)-presentable for some regular cardinal \(α_X\).
|
||||||
\item[(\dagger)] Every \(X ∈ \M\) is \(α_X\)-bounded with respect to some proper, well-copowered
|
% \item[(\dagger)] Every \(X ∈ \M\) is \(α_X\)-bounded with respect to some proper, well-copowered
|
||||||
orthogonal factorization system on \(\M\), for some regular cardinal \(α_X\).
|
% orthogonal factorization system on \(\M\), for some regular cardinal \(α_X\).
|
||||||
\end{itemize}
|
% \end{itemize}
|
||||||
Let \( J : \mathcal{J} → \M^→\) be a category over \(\M^→\), with \(\mathcal{J}\) small. Then the free awfs on \(\mathcal{J}\) exists
|
% Let \( J : \mathcal{J} → \M^→\) be a category over \(\M^→\), with \(\mathcal{J}\) small. Then the free awfs on \(\mathcal{J}\) exists
|
||||||
and is algebraically-free on \(\mathcal{J}\).
|
% and is algebraically-free on \(\mathcal{J}\).
|
||||||
\end{theorem}
|
% \end{theorem}
|
||||||
Without going to much into the size issues, every locally presentable categoy satisfies \((\ast)\). And as \(\□\) is a presheaf
|
% Without going to much into the size issues, every locally presentable categoy satisfies \((\ast)\). And as \(\□\) is a presheaf
|
||||||
category over a countable category, it is locally presentable. Also by beeing a presheaf category makes it automatically cocomplete.
|
% category over a countable category, it is locally presentable. Also by beeing a presheaf category makes it automatically cocomplete.
|
||||||
|
%
|
||||||
We also won't clarify all the consequences that getting an awfs instead of a wfs, brings with it. For us the important
|
% We also won't clarify all the consequences that getting an awfs instead of a wfs, brings with it. For us the important
|
||||||
thing is, that every awfs has an underlying wfs. The free part of that statement unsures that this construction preserves
|
% thing is, that every awfs has an underlying wfs. The free part of that statement unsures that this construction preserves
|
||||||
the right lifting class.
|
% the right lifting class.
|
||||||
|
%
|
||||||
Now we need to formulate our definitions in a way that agrees with this conditions of this theorem.
|
% Now we need to formulate our definitions in a way that agrees with this conditions of this theorem.
|
||||||
|
%
|
||||||
|
|
||||||
|
|
||||||
\subsubsection{Cofibrations and trivial fibrations}
|
\subsubsection{Cofibrations and trivial fibrations}
|
||||||
The short way of specifying this weak factorization system, is by saying
|
The short way of specifying this weak factorization system, is by saying
|
||||||
the cofibrations are the monomorphisms. Another, longer way, but for the further development more
|
the cofibrations are the monomorphisms. Another, longer way, but for the further development more
|
||||||
enlightening is by formulating this as uniform lifting properties.
|
enlightening is by formulating this as uniform lifting properties.
|
||||||
|
It is also not equivalent from the viewpoint of an awfs, as this definition has extra conditions on the
|
||||||
|
chosen lifts.
|
||||||
The condition to have uniform lifts, comes from \cite{CCHM} and generalized in \cite{gambinoFrobeniusConditionRight2017} . This requirement is motivated to have
|
The condition to have uniform lifts, comes from \cite{CCHM} and generalized in \cite{gambinoFrobeniusConditionRight2017} . This requirement is motivated to have
|
||||||
constructive interpretation of Cubical type theory. As we don't focus on the typetheoretic interpretation, but on the model structure we won't
|
constructive interpretation of Cubical type theory\todo{see ctt intro chapter when it is done}. As we don't focus on the typetheoretic interpretation, but on the model structure we won't
|
||||||
explore this further.
|
explore this further.
|
||||||
|
|
||||||
\begin{definition}
|
\begin{definition}
|
||||||
Let \(\mathcal{M}\) be a pullback stable class of morphisms.
|
Let \(J : \mathcal{M} ↣ \A^→\) be subcategory which objects are a pullback stable class of morphisms in \A, and morphisms are
|
||||||
A map \(f\) has the \emph{uniform right lifting property} against a \(\mathcal{M}\), if for every \(m ∈ \mathcal{M}\)
|
the cartesian squares between them. The category \(J^⧄\) is called the category \emph{uniform right lifting morphisms} with respect
|
||||||
every lifting problem of the form
|
to \(\mathcal{M}\). Objects of \(J^⧄\) are said to have the \emph{uniform right lifting property}.
|
||||||
\begin{equation*}
|
|
||||||
\begin{tikzcd}[column sep=large]
|
|
||||||
A \arrow[r,"α"] \arrow[d,"m"'] & X \arrow[d,"f"] \\
|
|
||||||
B \arrow[r,"β"] \arrow[ur, dashed, "{j(α,β)}"] & Y
|
|
||||||
\end{tikzcd}
|
|
||||||
\end{equation*}
|
|
||||||
has a specified solution, such that for every pullback square the following diagram with the specified
|
|
||||||
lifts commute.
|
|
||||||
\begin{equation*}
|
|
||||||
\begin{tikzcd}[column sep=large]
|
|
||||||
C \arrow[r,"a"] \arrow[d,"m'"] \pb & A \arrow[r, "α"] \arrow[d, "m"] & X \arrow[d,"f"] \\
|
|
||||||
D \arrow[r,"b"'] \arrow[urr,dashed,"{j(αa,βb)}"] & B \arrow[ur, dashed, "{j(α,β)}"'] \arrow[r,"β"'] & Y
|
|
||||||
\end{tikzcd}
|
|
||||||
\end{equation*}
|
|
||||||
\end{definition}
|
\end{definition}
|
||||||
|
|
||||||
\begin{definition}
|
|
||||||
A \emph{generating cofibration} is a monomorphism into a cube \(c : C ↣ \I^n\)
|
|
||||||
\end{definition}
|
|
||||||
|
|
||||||
\begin{definition}
|
|
||||||
A \emph{uniform trivial fibration} is a map with the uniform right lifting property against the generating cofibrations.
|
|
||||||
\end{definition}
|
|
||||||
|
|
||||||
Alternatively a definition more in line with our discussion above
|
|
||||||
|
|
||||||
\begin{definition}
|
\begin{definition}
|
||||||
The category of \emph{uniform generating cofibrations} has as object monomorphisms into a cube \(C ↣ I^n\) of arbitraty dimension, and
|
The category of \emph{uniform generating cofibrations} has as object monomorphisms into a cube \(C ↣ I^n\) of arbitraty dimension, and
|
||||||
as morphism cartesian squares between those.
|
as morphism cartesian squares between those.
|
||||||
|
@ -148,18 +126,18 @@ Alternatively a definition more in line with our discussion above
|
||||||
into \(\□^→\)
|
into \(\□^→\)
|
||||||
\end{definition}
|
\end{definition}
|
||||||
|
|
||||||
% TODO show equivalence in a rigorous way.
|
\todo{show that the cofib are all monos}
|
||||||
|
|
||||||
|
|
||||||
\subsubsection{Trivial cofibrations and fibrations}
|
\subsubsection{Trivial cofibrations and fibrations}
|
||||||
|
|
||||||
As we sketced above, the strategy will be to make more maps trivial cofibrations. This is done
|
As we sketched above, the strategy will be to make more maps trivial cofibrations. This is done
|
||||||
by making it harder to be a fibration. Before we give the definition in full generality, we
|
by making it harder to be a fibration. Before we give the definition in full generality, we
|
||||||
need to adress which coequilizer we talk about percisely.
|
need to adress which coequilizer we talk about percisely.
|
||||||
|
|
||||||
Of course doing this only in the 2 dimensional case is not enough. For this we need to say what
|
Of course doing this only in the 2 dimensional case is not enough. For this we need to say what
|
||||||
the “swap” maps are. What these should do is permutating the dimensions. So let \(Σ_k\) be the symmetric group
|
the “swap” maps are. What these should do is permutating the dimensions. So let \(Σ_k\) be the symmetric group
|
||||||
on \(k\) elements. For every \(σ' ∈ Σ_k\), we get a map from \( σ : \I^k → \I^k \), by \(⟨π_{σ'(1)}, … , π_{σ'(k)}⟩\),
|
on \(k\) elements. For every \(σ' ∈ Σ_k\), we get a map from \( σ : \I^k → \I^k \), by \((π_{σ'(1)}, … , π_{σ'(k)})\),
|
||||||
where \(π_l : \I^k → \I \) is the \(l\)-th projection. Also if we have a subcube \(f : \I^n \rightarrowtail \I^k\),
|
where \(π_l : \I^k → \I \) is the \(l\)-th projection. Also if we have a subcube \(f : \I^n \rightarrowtail \I^k\),
|
||||||
we get a pullback square of the following form
|
we get a pullback square of the following form
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
|
@ -170,7 +148,7 @@ we get a pullback square of the following form
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
whose right arrow we call \(σf\).
|
whose right arrow we call \(σf\).
|
||||||
%
|
%
|
||||||
Now we desrcibe our generating trivial cofibrations. We remeber example \ref{Leibniz:Ex:OpenBox}. We would
|
Now we desrcibe our generating trivial cofibrations. We remeber example \cref{Leibniz:Ex:OpenBox}. We would
|
||||||
like to do the same here, but a bit more general.
|
like to do the same here, but a bit more general.
|
||||||
|
|
||||||
|
|
||||||
|
@ -272,7 +250,7 @@ Now we can finaly give the definition of uniform equivariant fibrations.
|
||||||
|
|
||||||
\begin{definition}
|
\begin{definition}
|
||||||
The category of \emph{generating uniform equivariant trivial cofibrations} has as object
|
The category of \emph{generating uniform equivariant trivial cofibrations} has as object
|
||||||
generating cofibrations and as morphism squares of the shape defined in \ref{devilSquare}
|
generating cofibrations and as morphism squares of the shape defined in \cref{devilSquare}
|
||||||
above.
|
above.
|
||||||
\end{definition}
|
\end{definition}
|
||||||
\begin{definition}
|
\begin{definition}
|
||||||
|
@ -280,26 +258,401 @@ Now we can finaly give the definition of uniform equivariant fibrations.
|
||||||
uniform equivariant trivial cofibrations into \(\□^→\).
|
uniform equivariant trivial cofibrations into \(\□^→\).
|
||||||
\end{definition}
|
\end{definition}
|
||||||
|
|
||||||
|
\begin{notation}
|
||||||
|
By \cref{awfs:smallObject} these categories of maps form an awfs. We call it \((\TCF,\FF)\) and the underlying wfs
|
||||||
|
\((\Ct,\F)\)
|
||||||
|
\end{notation}
|
||||||
|
|
||||||
We will show that this is a modelstructure by using the theory of premodel structures
|
We will show that this is a modelstructure by using the theory of premodel structures
|
||||||
\cites[section 3]{cavalloRelativeEleganceCartesian2022}[section 3]{solution}{sattlerCYLINDRICALMODELSTRUCTURES}.
|
\cites{bartonModel2CategoryEnriched2019}[section 3]{cavalloRelativeEleganceCartesian2022}[section 3]{solution}{sattlerCYLINDRICALMODELSTRUCTURES}.
|
||||||
\todo{if there is time (there probably won't be) include the premodel theory and explain}
|
\todo{if there is time (there probably won't be) include the premodel theory and explain}
|
||||||
|
This machinery gives us a nice condition to check if we are actually dealing with a modelstructure. But first we need to
|
||||||
|
introduce the notion of a premodel structure.
|
||||||
|
|
||||||
This machinery gives us a nice condition to check if we are actually dealing with a modelstructure.
|
\begin{definition}[{\cites{bartonModel2CategoryEnriched2019}[def. 3.1.1]{cavalloRelativeEleganceCartesian2022}}]\label{def:preModelStructure}
|
||||||
|
A \emph{premodel Structure} on a finitely cocomplete and complete category \M consists of two weak factorization systems
|
||||||
|
\((C,F_t)\) (the \emph{cofibrations} and \emph{trivial fibrations}) and \((C_t, F)\) (the \emph{trivial cofibrations} and \emph{fibrations})
|
||||||
|
on \M such that \(C_t ⊆ C\) (or equivalently \(F_t ⊆ F\) ).
|
||||||
|
\end{definition}
|
||||||
|
|
||||||
\begin{theorem}[{\cite[theorem 3.3.5]{cavalloRelativeEleganceCartesian2022}}]\label{thm:premodelIsModel}
|
And also the definition of a property of such.
|
||||||
Let \(M\) be a cylindrical premodel category in which
|
\begin{definition}[{\cite[Definition 3.3.3]{cavalloRelativeEleganceCartesian2022}}]
|
||||||
|
We say a premodel category \M has the fibration extension property when for any fibration
|
||||||
|
\(f : Y → X\) and trivial cofibration \(m : X → X′\), there exists a fibration \(f' : Y' → X'\) whose base change along \(m\) is
|
||||||
|
\(f\):
|
||||||
|
\begin{eqcd*}[row sep=large, column sep=large]
|
||||||
|
Y \arrow[r,dashed] \arrow[d,"f"] \pb & Y' \arrow[d,dashed, "f'"] \\
|
||||||
|
X \arrow[r,"m"] & X'
|
||||||
|
\end{eqcd*}
|
||||||
|
\end{definition}
|
||||||
|
|
||||||
|
\begin{definition}[{\cite[Definition 3.2.5]{cavalloRelativeEleganceCartesian2022}}]
|
||||||
|
A \emph{cylindrical} premodel structure on a category E consists of a premodel structure
|
||||||
|
and adjoint functorial cylinder on E that are compatible in the following sense:
|
||||||
|
\begin{itemize}
|
||||||
|
\item \(∂ \⊗ (−)\) preserves cofibrations and trivial cofibrations;
|
||||||
|
\item \(δ_k \⊗ (−)\) sends cofibrations to trivial cofibrations for \(k ∈ \{0, 1\}\).
|
||||||
|
\end{itemize}
|
||||||
|
\end{definition}\todo{clean up and explain}
|
||||||
|
|
||||||
|
|
||||||
|
We get this characterizing theorem.
|
||||||
|
|
||||||
|
\begin{theorem}[{\cite[Theorem 3.3.5]{cavalloRelativeEleganceCartesian2022}}]\label{thm:premodelIsModel} \todo{if this gets longer expanded give it its own section}
|
||||||
|
Let \(\M\) be a cylindrical premodel category in which
|
||||||
\begin{enumerate}
|
\begin{enumerate}
|
||||||
\item all objects are cofibrant;
|
\item all objects are cofibrant;
|
||||||
\item the fibration extension property is satisfied.
|
\item the fibration extension property is satisfied.
|
||||||
\end{enumerate}
|
\end{enumerate}
|
||||||
Then the premodel structure on \(M\) defines a model structure.
|
Then the premodel structure on \(\M\) defines a model structure.
|
||||||
\end{theorem}
|
\end{theorem}
|
||||||
|
|
||||||
For this all to make sense we need to talk about what a \emph{cylindrical premodel} structure is, and what the
|
The first item is fast verified, as all monomorhpisms are cofibrations.\todo{make a small lemma to prove it (closure properties got you covered)}
|
||||||
\emph{fibration extension property} is.
|
The second condition we won't show directly. We will get for free if we construct fibrant universes, which we want to do anyway.
|
||||||
|
|
||||||
We will postpone to show that this is indeed a model structure with a univalent universe. First we will give a description
|
\subsubsection{Fibrant Universes}
|
||||||
for a model structure on the Dedekind cubes.
|
In this section we will change notation between commutative diagrams and the internal language of our presheaf.
|
||||||
|
As these tools can get quite technical and tedious to verify, we will only present the idea how these constructions
|
||||||
|
work and refer for the technical details to the source material.
|
||||||
|
|
||||||
|
The general construction of these universes follow mostly the same idea. We lift a Grothendieck universe from \Set to
|
||||||
|
the desired presheaf category, obtaining a Hofmann-Streicher universe \cite{hofmannLiftingGrothendieckUniverses1997},
|
||||||
|
classifying small maps.
|
||||||
|
This works in general for any presheaf topos over a small site. Afterwards we restrict this universe to only small fibrations.
|
||||||
|
We are then faced with a challenge, we need to prove that the resulting classifier is itself a fibration. In some cases
|
||||||
|
this can be made easier or avoided by stating this construction in a specific way.
|
||||||
|
|
||||||
|
For example by the arguments in \cite[Section 7]{awodeyHofmannStreicherUniverses2023} it suffices to construct \emph{classifying types}.
|
||||||
|
\begin{definition}\label{def:modelStructure:classifyingType}
|
||||||
|
A \emph{classifying type} for an awfs is a construction \(\Fib\) such that for every object \(X\)
|
||||||
|
and every morphism \(f : A → X\) there is a map \({\Fib(f) : \Fib(A) → X}\) and the section are in correspondence with
|
||||||
|
\(\mathrm{R}\)-algebra structures on \(f\).
|
||||||
|
Given a map \(g : Y → X\) then \(\Fib\) is stable under
|
||||||
|
pullbacks along \(g\).
|
||||||
|
\begin{eqcd*}[row sep=large]
|
||||||
|
g^*A
|
||||||
|
\arrow[r]
|
||||||
|
\arrow[d, "g^*f"']
|
||||||
|
\pb
|
||||||
|
& A
|
||||||
|
\arrow[d, "f"]
|
||||||
|
\\
|
||||||
|
Y
|
||||||
|
\arrow[r,"g"]
|
||||||
|
& X
|
||||||
|
\\
|
||||||
|
\Fib(g^*A)
|
||||||
|
\arrow[u, "\Fib(g^*f)"]
|
||||||
|
\arrow[r]
|
||||||
|
\arrow[ur,"\urcorner",phantom, very near start]
|
||||||
|
& \Fib(A)
|
||||||
|
\arrow[u, "\Fib(f)"']
|
||||||
|
\end{eqcd*}
|
||||||
|
\end{definition}
|
||||||
|
If the wfs, for that we try to classify the right maps, is functorial we might think of this as an internaliztaion
|
||||||
|
of the \(\R\)-algbera structures on \(f\).
|
||||||
|
|
||||||
|
We will first construct classifying types, after that we construct universes from it.
|
||||||
|
|
||||||
|
In preperation of the fibrant case we will first classify the trivial fibrations.
|
||||||
|
We don't have any equivariance condition on them, and thus they are the same as in \cite[Section 2]{awodeyCartesianCubicalModel2023},
|
||||||
|
when we assume \(Φ = Ω\).
|
||||||
|
|
||||||
|
Let us first think about the easiest case where the domain of auf trivial fibration is the terminal.
|
||||||
|
We should ask us what are the \TFF-algebra structures\todo{introduce notion above}. These are intuitively
|
||||||
|
choice functions of uniform liftings against cofibrations. So let us think about them first. If we picture
|
||||||
|
a lifting problem,
|
||||||
|
\begin{eqcd}\label{diag:liftProbTerminal}
|
||||||
|
A \arrow[d, tail] \arrow[r] & X \arrow[d] \\
|
||||||
|
C \arrow[r] & *
|
||||||
|
\end{eqcd}
|
||||||
|
we might think of this as a filling porblem of some shape \(A\) in \(X\) to some shape \(C\) in \(X\).
|
||||||
|
Or in other words as a complition of a partial map\footnote{Recall that a partial map \(C → X\) is a span \(C \leftarrow A → X\),
|
||||||
|
where the left map is a monomorphism.} from \(C → X\). We can classify these these by the partial map classifier,
|
||||||
|
given by \(X^+ ≔ Σ_{φ:Ω}X^{[φ]}\)\todo{give a reference}. This is gives us an object \(X^+\) (technicaly equipped with a map into the terminal)
|
||||||
|
and a monomrphism \( η_X : X → X^+\) such that for evey partial map \(C → X\) there is a unique map \(a: C → X^+\) completing
|
||||||
|
the following pullback square.
|
||||||
|
\begin{eqcd*}
|
||||||
|
A \arrow[d, tail] \arrow[r] \pb & X \arrow[d,"η_X"] \\
|
||||||
|
C \arrow[r, "a"] & X^+
|
||||||
|
\end{eqcd*}
|
||||||
|
This makes \((−)^+\) into a pointed endofunctor, and with little surprise are the \(+\)-algebras in correspondence with
|
||||||
|
the \TFF-algebras.
|
||||||
|
|
||||||
|
\begin{proposition}[{\cite[Proposition 15]{awodeyCartesianCubicalModel2023}}]
|
||||||
|
The algebras of the pointed endofunctor \((−)^+\) are in correspondence to the algebras of the pointed endofunctor \TFF
|
||||||
|
with codomain \(*\).
|
||||||
|
\end{proposition}
|
||||||
|
\begin{proof}[Proofsketch:]
|
||||||
|
A \(+\)-algebra is an object \(X\) together with a morphism \(α : X^+ → X\) such that \(α η_x = \id\).
|
||||||
|
Take some lifting problem like \cref{diag:liftProbTerminal}, define the chosen map to be \(αa\). If we
|
||||||
|
are given a chosen lift, we compose it with \(η_X\) to retrieve \(a\).
|
||||||
|
\end{proof}
|
||||||
|
|
||||||
|
The benefit of \((−)^+\)-algebras is, that they are morphisms in \□ rather than in \(\□^→\).
|
||||||
|
We can interalize the condition to be a \((−)^+\)-algebra by means of the internal \(\Hom\).
|
||||||
|
\begin{eqcd*}
|
||||||
|
+\textrm{-Alg}(X)
|
||||||
|
\arrow[d]
|
||||||
|
\arrow[r]
|
||||||
|
\pb
|
||||||
|
& {[X^+,X]}
|
||||||
|
\arrow[d,"{[η_X,\id_X]}"]
|
||||||
|
\\
|
||||||
|
*
|
||||||
|
\arrow[r,"λ\id_X"]
|
||||||
|
& {[X,X]}
|
||||||
|
\end{eqcd*}
|
||||||
|
It is immediatly clear that a sections of the left map correspond to the desired \(+\)-algebra structure.
|
||||||
|
|
||||||
|
If we want to archive the same with a trivial fibration that has arbitrary codomain \(Y\), we might just move
|
||||||
|
to the slice topos \(\faktor{\□}{Y}\), there such a map becomes again a map into the terminal.
|
||||||
|
To not be confused we will call the partial map classification functor in
|
||||||
|
the slice over \(Y\) by the name \((−)^{+Y}\). The algebras will be called relative \(+\)-algberas.
|
||||||
|
We have even more luck and this functor commutes with the pullback
|
||||||
|
functor \(\□ → \faktor{\□}{Y}\),
|
||||||
|
\begin{eqcd*}
|
||||||
|
\faktor{\□}{Y}
|
||||||
|
\arrow[r, "(−)^{+Y}"]
|
||||||
|
& \faktor{\□}{Y}
|
||||||
|
\\
|
||||||
|
\□
|
||||||
|
\arrow[u,"Y^*"]
|
||||||
|
\arrow[r,"(−)^+"]
|
||||||
|
& \□
|
||||||
|
\arrow[u,"Y^*"]
|
||||||
|
\end{eqcd*}
|
||||||
|
which allows us to compute it fiberwise \cite[Proposition 12]{awodeyCartesianCubicalModel2023}. This allows us to write
|
||||||
|
\((A)^{+Y} = Σ_{y:Y}A_y^+\), where \(A_y\) is the fiber of \(A\) at \(y\). We will still continue to write \(+\)-Alg, when
|
||||||
|
there is no confusion.
|
||||||
|
As all the involved functors \((−)^+\), pullbacks and exponentials are pullback stable so is \(+\)-Alg. Wich lets us conlude
|
||||||
|
the following.
|
||||||
|
\begin{proposition}
|
||||||
|
\(+\)-Alg is a classifying type for trivial cofibrations.
|
||||||
|
\end{proposition}
|
||||||
|
|
||||||
|
|
||||||
|
We will move down a very similar path as \cite{awodeyCartesianCubicalModel2023}, but need to keep track of the group
|
||||||
|
actions of the symmetric groups on representables.
|
||||||
|
For this we will pass to a category that \cite{solution} calls cubical species. The argument in essence will be very similar
|
||||||
|
to the argument there, though in a different language.
|
||||||
|
|
||||||
|
\begin{definition}[compare {\cite[Section 4]{solution}}]
|
||||||
|
By abuse of notation we will say \(Σ_k\) to be the one object groupoid induced by the symmetric group \(Σ_k\).
|
||||||
|
Let \(Σ ≔ ∐_{k ∈ ℕ} Σ_k\), we define \(\□^Σ\) to be the category of \emph{cubical species}. For a cubical
|
||||||
|
species \(A\) we write \(A_k\) for the cubical set in the image of \(Σ_k\).
|
||||||
|
\end{definition}
|
||||||
|
\begin{remark}
|
||||||
|
\(\□^Σ\) is a presheaf topos.
|
||||||
|
\end{remark}
|
||||||
|
\begin{remark}
|
||||||
|
\cite{solution} excludes the case for \(k = 0\), because they want to exhibit a model category on cubical species.
|
||||||
|
For the construction on cubical Sets this makes no difference compare \cite[Remark 4.3.17]{solution}.
|
||||||
|
\end{remark}
|
||||||
|
\begin{remark}
|
||||||
|
Going forward we keep the names trivial fibrations,cofibrations, fibrationstructure, \dots, even though we don't
|
||||||
|
have defined any of this notions on \(\□^Σ\). We mean the objects that are equivalently classified in this
|
||||||
|
topos, like in the procedure above. This can actually be made into a modelstructure where these are the corresponding
|
||||||
|
fibrations, cofibrations, \dots, for details see \cite[Section 4]{solution}.
|
||||||
|
\end{remark}
|
||||||
|
|
||||||
|
We need to define our equivalent of an interval, and the generic point inclusion. Recall that a functor from a group
|
||||||
|
into a category is the same as choosing an object of that category together with a group action on it.
|
||||||
|
\begin{definition}[{\cite[Example 4.3.5]{solution}}]
|
||||||
|
Let \(\mathrm{I} : Σ → \□\) be the functor that sends \(Σ_k\) to \(\I^k\) together with the group action that freely
|
||||||
|
permutates the dimensions.
|
||||||
|
\end{definition}
|
||||||
|
\begin{remark}[{\cite[Lemma 4.2.7]{solution}}]
|
||||||
|
The interval \(\mathrm{I}\) is tiny.
|
||||||
|
\end{remark}
|
||||||
|
|
||||||
|
\begin{definition}[{\cite[Definition 4.3.3]{solution}}]
|
||||||
|
The diagonal \(δ : \mathrm{I} → \mathrm{I} × \mathrm{I}\) as a map in the slice \(\faktor{\□^Σ}{\mathrm{I}}\) is called
|
||||||
|
the generic point.
|
||||||
|
\end{definition}
|
||||||
|
|
||||||
|
% We will classify what in \cite{awodeyCartesianCubicalModel2023} would be called biased fibrations with regard to \(δ_0\) in \(\□^Σ\).
|
||||||
|
% These are not the kind of fibrations we are interested in, as we want lifts against the generic point. We will sort that out later.
|
||||||
|
% As the monic maps in \(\□^Σ\) are precisely those that are componentwise monic, we are just going to characterize
|
||||||
|
% componentwise fibrations. But because we passed to \(\□^Σ\), the classifying type will have group actions on
|
||||||
|
% every level, and we need to restrict to those, that are invariant under those group actions.
|
||||||
|
|
||||||
|
The main idea to continue classifying uniform fibrations from here on out is quite simple. As being a uniform fibration is
|
||||||
|
equivalent by being send to a trivial fibration by the right adjoint of the leibniz applicationfunctor of the inteval,
|
||||||
|
we get that a \(+\)-algebra structure on \(δ ⇒ f\)\todo{write the right thing here}
|
||||||
|
is equivalent to a \FF-algebra structure on \(f\). This must then
|
||||||
|
be reformulated, to get the desired map. This reformulation is quite tedious and so we will refer
|
||||||
|
for the details to
|
||||||
|
\cite[The classifying types of unbiased fibration structures]{awodeyCartesianCubicalModel2023}.
|
||||||
|
In the source this takes place in \□, but it only makes use of the features we already established for \(\□^Σ\).
|
||||||
|
An important detail
|
||||||
|
to this procedure is, that in order to get the resulting classifying type pullback stable, this argument uses that
|
||||||
|
the interval is tiny.
|
||||||
|
|
||||||
|
We get a pullback stable construction \(\Fib^Σ(f)\)\footnote{this can be made into a classifying type for some
|
||||||
|
awfs compare \cite[Section 4.]{solution}}\todo{this footnote 2 is bad, but how to make different}
|
||||||
|
whose sections now correspond componentwise to \FF-algebra structures, that are equivariant with respect
|
||||||
|
to the group action of \(Σ^k\).
|
||||||
|
|
||||||
|
We now going to extract the classifying type for equivariant cubical fibrations. For this we need to relate cubical sets
|
||||||
|
and cubical species. There exists the constant diagram functor \(Δ\) that sends a cubical set to the constant cubical species.
|
||||||
|
|
||||||
|
|
||||||
|
Since \□ is complete this functor has a right adjoint\footnote{and also a left adjoint as \□ is cocomplete}
|
||||||
|
\(Γ\) compare \cite[Section 5.1]{solution}, which is given by
|
||||||
|
|
||||||
|
\begin{equation*}
|
||||||
|
Γ(A) ≔ ∏\limits_{k∈ℕ}(A_k)^{Σ_k}
|
||||||
|
\end{equation*}
|
||||||
|
|
||||||
|
where \((A_k)^Σ_k\) is the cubical set of \(Σ_k\) fixed points. It is not hard to see that this is indeed
|
||||||
|
the right adjoint functor.
|
||||||
|
|
||||||
|
\begin{proposition}
|
||||||
|
We have a pair of adjoints \(Δ ⊣ Γ\)
|
||||||
|
\end{proposition}
|
||||||
|
\begin{proof}
|
||||||
|
We need to show
|
||||||
|
\begin{equation*}
|
||||||
|
\Hom_{\□^Σ}(Δ(A),B) = \Hom_{\□}\left(A,∏\limits_{k∈ℕ}(B_k)^{Σ_k}\right) \text{.}
|
||||||
|
\end{equation*}
|
||||||
|
But this is immediatly clear, on the right hand side we have componentwise equivariant natural translations
|
||||||
|
from \(Δ(A)_k = A\) to \(B_k\). They can only be valued in the fixed points in \(B_k\) as \(Δ(A)_k\) carries the
|
||||||
|
trivial group action. A map on the right side is also a collection of natural transformations from \(A\) to
|
||||||
|
the fixed points of \(B_k\).
|
||||||
|
\end{proof}
|
||||||
|
|
||||||
|
We get now that an \FF-algebra on \(f : A → B\) structure corresponds to a section
|
||||||
|
\begin{eqcd*}
|
||||||
|
{} & \mathrm{Fib}^{Σ_k}(Δ(A))
|
||||||
|
\arrow[d,"\mathrm{Fib}^{Σ_k}(Δ(f))"]
|
||||||
|
\\ Δ(B) \arrow[r,equal]
|
||||||
|
\arrow[ru, dashed]
|
||||||
|
& Δ(B)
|
||||||
|
\end{eqcd*}
|
||||||
|
By adjointness we can transpose this lift to a lift in cubical sets, and by pulling back
|
||||||
|
along the adjunction unit to splits of a map over \(B\) (compare \cite[Lemma 5.3.3,2.1.16]{solution}).
|
||||||
|
\begin{eqcd*}[row sep=large]
|
||||||
|
\mathrm{Fib}(B)
|
||||||
|
\arrow[d,"\mathrm{Fib}(f)"]
|
||||||
|
\arrow[r]
|
||||||
|
\pb
|
||||||
|
& Γ(\mathrm{Fib}^{Σ_k}(Δ(A)))
|
||||||
|
\arrow[d,"Γ(\mathrm{Fib}^{Σ_k}(Δ(f)))"]
|
||||||
|
\\ B \arrow[r,"η_B"]
|
||||||
|
\arrow[ru, dashed]
|
||||||
|
\arrow[u,bend left, dashed]
|
||||||
|
& ΓΔ(B)
|
||||||
|
\end{eqcd*}
|
||||||
|
|
||||||
|
We will now present the main idea, how to get fibrant universes from such classifying types.
|
||||||
|
The technical details can be found in \cite[Section 7]{awodeyHofmannStreicherUniverses2023}.
|
||||||
|
One might hope that we can construct a universal fibration, in the sense that every fibration
|
||||||
|
is a pullback of this universal fibration. This can not happen for size reasons. We will do
|
||||||
|
the next best thing and construct a universe for big enough kardinals \(κ\). Because
|
||||||
|
our set theory has Grothendieck universes this will give us universes for \(κ\) small maps fibrations.
|
||||||
|
|
||||||
|
To start we will call our Hofmann-Streicher, or \(κ\)-small map classifier, \({p : \dot{\mathcal{V}}_κ → \mathcal{V}_κ}\).
|
||||||
|
|
||||||
|
\begin{proposition}[{\cite[Proposition 10]{awodeyHofmannStreicherUniverses2023}}]
|
||||||
|
For a large enough \(κ\), there is a universe for \(κ\)-small fibrant maps, in the sense that there is
|
||||||
|
a small fibration \(π : \dot{\mathcal{U}}_κ → \mathcal{U}_κ\) such that every small fibration \(f : A → X\), is
|
||||||
|
a pullback of it along a connonical classifying map \(a\)
|
||||||
|
\begin{eqcd*}
|
||||||
|
A
|
||||||
|
\pb
|
||||||
|
\arrow[d,"f"]
|
||||||
|
\arrow[r]
|
||||||
|
& \dot{\mathcal{U}}_{κ}
|
||||||
|
\arrow[d,"π_κ"]
|
||||||
|
\\
|
||||||
|
\mathcal{X}
|
||||||
|
\arrow[r,"a"]
|
||||||
|
& \mathcal{U}
|
||||||
|
\end{eqcd*}
|
||||||
|
\end{proposition}
|
||||||
|
|
||||||
|
\begin{proof}
|
||||||
|
We can then construct our universe that classifies \(κ\)-small fibrations by setting \(\mathcal{U}_κ ≔ \mathrm{Fib}(\dot{\mathcal{V}}_κ)\)
|
||||||
|
and building the following pullback.
|
||||||
|
\begin{eqcd*}[row sep=large, column sep = large]
|
||||||
|
\dot{\mathcal{U}}_κ
|
||||||
|
\pb
|
||||||
|
\arrow[d,"π_κ"]
|
||||||
|
\arrow[r]
|
||||||
|
& \dot{\mathcal{V}}_{κ}
|
||||||
|
\arrow[d,"p"]
|
||||||
|
\\
|
||||||
|
\mathcal{U}
|
||||||
|
\arrow[r,"\mathrm{Fib}(p)"]
|
||||||
|
& \mathcal{V}
|
||||||
|
\end{eqcd*}
|
||||||
|
To see this is a fibration we will exhibit we exhibit a split of the classifying type of \(π_κ\).
|
||||||
|
As the classifying type is pullback stable we get the following diagram
|
||||||
|
\begin{eqcd*}[row sep=large, column sep = large]
|
||||||
|
\dot{\mathcal{U}}_κ
|
||||||
|
\pb
|
||||||
|
\arrow[d,"π_κ"]
|
||||||
|
\arrow[r]
|
||||||
|
& \dot{\mathcal{V}}_{κ}
|
||||||
|
\arrow[d,"p"]
|
||||||
|
\\
|
||||||
|
\mathcal{U_κ}
|
||||||
|
\arrow[r,"\mathrm{Fib}(p)"]
|
||||||
|
& \mathcal{V_κ}
|
||||||
|
\\
|
||||||
|
\mathrm{Fib}(\dot{\mathcal{U}}_κ)
|
||||||
|
\arrow[u]
|
||||||
|
\arrow[r]
|
||||||
|
\arrow[ur,phantom,very near start,"\urcorner"]
|
||||||
|
& \mathrm{Fib}(\dot{\mathcal{V}}_κ)
|
||||||
|
\arrow[u,"\mathrm{Fib}(p)"]
|
||||||
|
\end{eqcd*}
|
||||||
|
The lower pullback square is a pullback of \(\Fib(p)\) along itself. This map has a split, namely the diagonal.
|
||||||
|
To show that this classifies small fibrations, let us consider a small fibration \(f : A → X\).
|
||||||
|
Because it is a small map we get it as a pull back along a cannonical map \(a : X → \mathcal{V}\).
|
||||||
|
\begin{eqcd*}
|
||||||
|
{}
|
||||||
|
& {}
|
||||||
|
& \dot{\mathcal{U}}
|
||||||
|
\arrow[dr]
|
||||||
|
\arrow[dd]
|
||||||
|
&
|
||||||
|
\\
|
||||||
|
{}
|
||||||
|
& |[alias=A]| A
|
||||||
|
\arrow[rr,crossing over]
|
||||||
|
\arrow[ru,dashed]
|
||||||
|
& & \dot{\mathcal{V}}
|
||||||
|
\arrow[dd]
|
||||||
|
\\
|
||||||
|
\Fib(A)
|
||||||
|
\arrow[rr]
|
||||||
|
\arrow[dr]
|
||||||
|
& & \mathcal{U}
|
||||||
|
\arrow[dr]
|
||||||
|
&
|
||||||
|
\\
|
||||||
|
{}
|
||||||
|
& |[alias=X]| X
|
||||||
|
\arrow[rr,"a"]
|
||||||
|
\arrow[lu,dashed,"s",bend left]
|
||||||
|
\arrow[ur,dashed,"s'"]
|
||||||
|
& & \mathcal{V}
|
||||||
|
\arrow[from=A,to=X,crossing over]
|
||||||
|
\end{eqcd*}
|
||||||
|
We get the lower square as a pullback as \Fib is pullback stable and \(\mathcal{U} = \Fib(\dot{\mathcal{V}})\).
|
||||||
|
As \(f\) is a fibration, we get a split \(s\) of the fibration structure. And so we get a unique corresponding map
|
||||||
|
\(s'\), which induces the required pullback square.
|
||||||
|
|
||||||
|
\end{proof}
|
||||||
|
|
||||||
|
\todo{introduce Leibniz pullback exponential}
|
||||||
|
\todo{introduced (unbiased) uniform fibrations and how they behave with leibniz constructions}
|
||||||
|
\todo{hate my life}
|
||||||
|
|
||||||
|
\subsubsection{HS-Universe}
|
||||||
|
Assume this as given for now, if we have time we can write this out \todo{delete it or write it out, and move it to some preliminary place}
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
|
|
|
@ -1,11 +1,11 @@
|
||||||
\documentclass[../Main.tex]{subfiles}
|
\documentclass[../Main.tex]{subfiles}
|
||||||
\begin{document}
|
\begin{document}
|
||||||
% \chapter{Preliminaries}
|
% \chapter{Preliminaries}
|
||||||
\section{Category Theory}
|
% \section{Category Theory}
|
||||||
We already assume some basic notions of category theory. For the completly unitiated there are good
|
% We already assume some basic notions of category theory. For the completly unitiated there are good
|
||||||
references for example \cite{maclaneCategoriesWorkingMathematician1978} or \cite{awodeyCategoryTheory2006}.
|
% references for example \cite{maclaneCategoriesWorkingMathematician1978} or \cite{awodeyCategoryTheory2006}.
|
||||||
We will also assume some familarities with presheave categories \cite{maclaneSheavesGeometryLogic1994}.
|
% We will also assume some familarities with presheave categories \cite{maclaneSheavesGeometryLogic1994}.
|
||||||
But we will revisit some branches of category theory that we will encouter later.
|
% But we will revisit some branches of category theory that we will encouter later.
|
||||||
|
|
||||||
|
|
||||||
% \subfile{Model_Categories}
|
% \subfile{Model_Categories}
|
||||||
|
|
|
@ -1,18 +1,20 @@
|
||||||
\documentclass[../Main.tex]{subfiles}
|
\documentclass[../Main.tex]{subfiles}
|
||||||
\begin{document}
|
\begin{document}
|
||||||
\section{Equivalence to spaces}\todo{do I need to explain idempotent completions?}
|
\section{Equivalence to spaces}\todo{\printline do I need to explain idempotent completions?}
|
||||||
|
\todo{give all natural transformations \(⇒\) instead of \(→\)}
|
||||||
|
|
||||||
For this section we fix the following notation. We write \(n\) for a set with cardinality \(n\),
|
For this section we fix the following notation. We write \(n\) for a set with cardinality \(n\),
|
||||||
and identify \(2\) with the set \(\{⊥,⊤\}\). Wen write \([n]\) for the well ordered sets
|
and identify \(2\) with the set \(\{⊥,⊤\}\). We write \([n]\) for the well ordered sets
|
||||||
\(\{0,…,n\}\).
|
\(\{0,…,n\}\).
|
||||||
|
|
||||||
We would love to compare the model categories on \(\□\) and \(\Δ\). For this we want at least
|
We would love to compare the model categories on \(\□\) and \(\Δ\). For this we want at least
|
||||||
an adjoint pair between those. If we somehow could get a functor on the site level, we could
|
an adjoint pair between those. If we somehow could get a functor on the site level, we could
|
||||||
get an adjoint triple. But there is no immediate obvious functor to do the job.
|
get an adjoint triple. But there is no immediate obvious functor to do the job.
|
||||||
The usual trick would be to go look at the idempotent completions of these categories. These
|
The usual trick would be to go look at the idempotent completions of these categories. These
|
||||||
have usually more objects and are sometimes more suitable as the codomain of a functor, while
|
usually have :w
|
||||||
|
more objects and are sometimes more suitable as the codomain of a functor, while
|
||||||
the presheaf category stays the same (up to equivalence).
|
the presheaf category stays the same (up to equivalence).
|
||||||
For example the idempotent completion of \dCube is the category \FL of finite lattices and
|
For example, the idempotent completion of \dCube is the category \FL of finite lattices and
|
||||||
monotone maps \cites{streicherSimplicialSetsCubical2021}{sattlerIdempotentCompletionCubes2019}.
|
monotone maps \cites{streicherSimplicialSetsCubical2021}{sattlerIdempotentCompletionCubes2019}.
|
||||||
So we have automatically \(\widehat{\FL} = \dcSet\),
|
So we have automatically \(\widehat{\FL} = \dcSet\),
|
||||||
and there is an obvious inclusion \(i: Δ → \FL\). Sadly for us \(□\) is already idempotent complete.
|
and there is an obvious inclusion \(i: Δ → \FL\). Sadly for us \(□\) is already idempotent complete.
|
||||||
|
@ -31,22 +33,22 @@ To get around this issue we can embed \(j: □ → \dCube → \FL\), and get int
|
||||||
\end{tikzcd}
|
\end{tikzcd}
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
|
|
||||||
We can define \(j\) also explicitly like this:
|
We can also define \(j\) explicitly like this:
|
||||||
\begin{definition}
|
\begin{definition}
|
||||||
Let \(𝟚\) the finite order \(⊥ ≤ ⊤\), if it is convenient we will identify this with the order \(0 ≤ 1\).
|
Let \(𝟚\) be the finite order \(⊥ ≤ ⊤\). If it is convenient we will identify this with the order \(0 ≤ 1\).
|
||||||
\end{definition} \todo{move this somewhere sane}
|
\end{definition} \todo{\printline move this somewhere sane}
|
||||||
|
|
||||||
\begin{definition}\label{def:j}
|
\begin{definition}\label{def:j}
|
||||||
Let \(j : □ → \FL\) the functor given by the following data:
|
Let \(j : □ → \FL\) the functor given by the following data:
|
||||||
\begin{itemize}
|
\begin{itemize}
|
||||||
\item On objects: \(f(\{⊥|x_1…x_n|⊤\}) ≔ 𝟚^n\) \todo{use \(⊥⊤\) notation in introduction chapter}
|
\item On objects: \(f(\{⊥|x_1…x_n|⊤\}) ≔ 𝟚^n\) \todo{\printline use \(⊥⊤\) notation in introduction chapter}
|
||||||
\item On morphisms: \(j(f)(g)(x) ≔ \begin{cases}g(f(x)) & f(x) \notin 𝟚 \\ f(x) & f(x) ∈ 𝟚\end{cases}\)
|
\item On morphisms: \(j(f)(g)(x) ≔ \begin{cases}g(f(x)) & f(x) \notin 𝟚 \\ f(x) & f(x) ∈ 𝟚\end{cases}\)
|
||||||
\end{itemize}
|
\end{itemize}
|
||||||
\end{definition}
|
\end{definition}
|
||||||
|
|
||||||
In \cite{rhielVid} it is claimed that \(i^*j_!\) is the triangulation functor and \(j^*i_!\) a
|
In \cite{riehlVid} it is claimed that \(i^*j_!\) is the triangulation functor and \(j^*i_!\) a
|
||||||
left Quillen homotpoy inverse. In the mean time Reid Barton observed in an yet unpublished paper,
|
left Quillen homotopy inverse. In the mean time Reid Barton observed in an yet unpublished paper,
|
||||||
\todo{how to cite this? claimed in \cite{solution}}
|
\todo{\printline how to cite this? claimed in \cite{solution}}
|
||||||
that this triangulation can be described by a single functor on the level of sites \(Δ → □\). One
|
that this triangulation can be described by a single functor on the level of sites \(Δ → □\). One
|
||||||
could now establish Quillen equivalence using this functor, for details see \cite[sec. 6]{solution}.
|
could now establish Quillen equivalence using this functor, for details see \cite[sec. 6]{solution}.
|
||||||
We are going to verify the original argument. To give an overview of the necessary steps:
|
We are going to verify the original argument. To give an overview of the necessary steps:
|
||||||
|
@ -58,17 +60,16 @@ We are going to verify the original argument. To give an overview of the necessa
|
||||||
\end{enumerate}
|
\end{enumerate}
|
||||||
|
|
||||||
Before we jump into the formal proofs we like to get some intuition for the four functors of interest.
|
Before we jump into the formal proofs we like to get some intuition for the four functors of interest.
|
||||||
To make sense of this all we need to understand what happens with \FL. \FL has the luxury as containing
|
The category \FL has the luxury as containing
|
||||||
both \(Δ\) as the well orderings and \dCube as \(𝟚^n\). As \FL is the idempotent completion of \dCube,
|
both \(Δ\) as the well orderings and \dCube as \(𝟚^n\). As \FL is the idempotent completion of \dCube,
|
||||||
we also now that a presheaf on \FL, is completly determined by its behavior on \dCube. The two functors
|
we also know that a presheaf on \FL is completely determined by its behavior on \dCube. The two functors
|
||||||
\(i^*\) and \(j^*\) are just the restrictions, but also \(i_!\) and \(j_!\) are geometrically not so
|
\(i^*\) and \(j^*\) are just the restrictions, and we can also understand \(i_!\) and \(j_!\) geometrically.
|
||||||
difficult to understand. On the elements in the image of \(i\) (or \(j\)) they agree with the original definition.
|
|
||||||
Let \(F ∈ \Δ\), then \(F(x) = i_!(F)(i(x))\). The interesting question is what does \(i_!\) define
|
Let \(F ∈ \Δ\), then \(F(x) = i_!(F)(i(x))\). The interesting question is what does \(i_!\) define
|
||||||
on cubes and \(j_!\) on simplicials. \(j_!\) will basically triangulate the cube (see \fref{prop:triangulation}),
|
on cubes (aka \(\Yo 𝟚^n\)) and \(j_!\) on simplicials (aka \(\Yo [n]\)). \(j_!\) will basically triangulate the cube (see \cref{prop:triangulation}),
|
||||||
while \(i_!\) will add just cubes that are degenerated to simplicials.
|
while \(i_!\) will add just all possible cubes that are degenerated to simplicials.
|
||||||
|
|
||||||
To understand \(i^*\) a bit better we might take a look how things that are defined on \(𝟚^n\) extend to simplicials.
|
To understand \(i^*\) a bit better we might take a look how things that are defined on \(𝟚^n\) extend to simplicials.
|
||||||
For this we need to exhibit \([n]\), as a retract of \(𝟚^n\). For this we define two maps.
|
For this we need to exhibit \([n]\) as a retract of \(𝟚^n\). For this we define two maps.
|
||||||
\begin{definition}
|
\begin{definition}
|
||||||
Let
|
Let
|
||||||
\begin{itemize}
|
\begin{itemize}
|
||||||
|
@ -77,60 +78,81 @@ For this we need to exhibit \([n]\), as a retract of \(𝟚^n\). For this we def
|
||||||
\end{itemize}
|
\end{itemize}
|
||||||
\end{definition}
|
\end{definition}
|
||||||
We can see directly that this is a split retract pair and thus gives rise to an idempotent \(e = ir : 𝟚^n → 𝟚^n\).
|
We can see directly that this is a split retract pair and thus gives rise to an idempotent \(e = ir : 𝟚^n → 𝟚^n\).
|
||||||
And by general abstract nonesens we get that \(r\) is an absolute coequilizer map of \(e\) and \(\id\). As well as \(i\)
|
And by general abstract nonsense we get that \(r\) is an absolute coequalizer map of \(e\) and \(\id\). Similarly \(i\)
|
||||||
is an aboslute equilizer of \(e\) and \(\id\). So for a presheaf
|
is an absolute equalizer of \(e\) and \(\id\). So for a presheaf
|
||||||
\(F\) on \FL, we can compute \(F([n])\) as the equilizer from \(F(e)\) and \(F(\id)\), or the coequilizer of \(F(e)\) and \(F(\id)\).
|
\(F\) on \FL, we can compute \(F([n])\) as the equalizer of \(F(e)\) and \(F(\id)\), or the coequalizer of \(F(e)\) and \(F(\id)\)
|
||||||
|
in \Set.
|
||||||
|
|
||||||
\begin{proposition}\label{prop:i_!Nothing}
|
\begin{proposition}\label{prop:i_!Nothing}
|
||||||
\(i_!Δ^n\) agrees with \(\Yo [n]\).
|
\(i_!Δ^n\) agrees with \(\Yo [n]\).
|
||||||
\end{proposition}
|
\end{proposition}
|
||||||
\begin{proof}
|
\begin{proof} We have
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
\Hom_{\FL}(i_!Δ^n,B) = \Hom_{\Δ}(Δ^n,i^*B) = B(i([n])) = B([n]) = \Hom_{\FL}(\Yo [n], B)
|
\Hom_{\FL}(i_!Δ^n,B) = \Hom_{\Δ}(Δ^n,i^*B) = B(i([n])) = B([n]) = \Hom_{\FL}(\Yo [n], B) \text{,}
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
And by uniqueness of adjoints the claim follows.
|
and by uniqueness of adjoints, the claim follows.
|
||||||
\end{proof}
|
\end{proof}
|
||||||
|
|
||||||
\begin{proposition}\label{prop:j_!Nothing}
|
\begin{proposition}\label{prop:j_!Nothing}
|
||||||
\(j_!(\I^n) = \Yo 𝟚^n\)
|
\(j_!(\I^n) = \Yo 𝟚^n\)
|
||||||
\end{proposition} \todo{move to a sane place}
|
\end{proposition} \todo{\printline move to a sane place}
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
We have that \(\Hom(j_!(\I^n),B) = \Hom(\I^n,j^*(B))\). And we get
|
We have that \(\Hom(j_!(\I^n),B) = \Hom(\I^n,j^*(B))\). And we get
|
||||||
\begin{equation}
|
\begin{equation*}
|
||||||
\Hom(\Yo 𝟚^n, B) = B(𝟚^n) = B(j(n)) = \Hom(\I^n,j^*B)
|
\Hom(\Yo 𝟚^n, B) = B(𝟚^n) = B(j(n)) = \Hom(\I^n,j^*B)\text{.}
|
||||||
\end{equation}
|
\end{equation*}
|
||||||
thus by uniqueness of adjoints we have, that \(j_!(\I^n) = \Yo 𝟚^n\).
|
Thus, by uniqueness of adjoints, we have that \(j_!(\I^n) = \Yo 𝟚^n\).
|
||||||
\end{proof}
|
\end{proof}
|
||||||
|
|
||||||
Let us start with step 1. We need to show that \(i_!\) and \(i^*\) preserve cofibrations (or
|
\subsection{\(i_!\) and \(i^*\) are left Quillen functors}
|
||||||
in other words monomorphisms), \(i^*\) preservers fibrations and trivial cofibrations. The hard
|
We need to show that \(i_!\) and \(i^*\) preserve cofibrations (or
|
||||||
part will be to show that \(i_!\) preserves monomorphisms and we will do it last.
|
in other words monomorphisms) and trivial cofibrations. The hard
|
||||||
|
part will be to show that \(i_!\) preserves monomorphisms and we will do that last.
|
||||||
|
|
||||||
\begin{proposition}
|
\begin{lemma}\label{lem:restrictionPreserveMonos}
|
||||||
|
Let \(F: \A → \B\) be a functor, then the restriction functor \(F^* : \hat{\B} → \hat{\A}\) preserves monomorphisms.
|
||||||
|
\end{lemma}
|
||||||
|
\begin{proof}
|
||||||
|
Let \(f\) be a monomorphism in \(\hat{\B}\). As being monic can be tested componentwise, we need
|
||||||
|
to show that \((i^*f)_x\) is monic for an arbitrary \(x∈\A\). This is just \(f_{(ix)}\) which is monic by assumption.
|
||||||
|
\end{proof}
|
||||||
|
|
||||||
|
\begin{proposition}\label{prop:i*preservesMonos}
|
||||||
\(i^*\) preserves monomorphisms.
|
\(i^*\) preserves monomorphisms.
|
||||||
\end{proposition}
|
\end{proposition}
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
Given a monomorphism \(f\) in \(\Δ\). As being monic can be tested component wise we need
|
Directly by \cref{lem:restrictionPreserveMonos}.
|
||||||
to show that \((i^*f)_x\) is monic, for an arbitrary \(x∈□\). This is just \(f_{(ix)}\) which is monic by assumption.
|
|
||||||
\end{proof}
|
\end{proof}
|
||||||
|
|
||||||
\begin{proposition}
|
\begin{proposition}\label{prop:i*preservesTrivialCofib}
|
||||||
\(i^*\) preserves trivial cofibrations \todo{maybe equivalently \(i_*\) preserves fibrations}
|
\(i^*\) preserves trivial cofibrations.
|
||||||
\end{proposition}
|
\end{proposition}
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
Sketch:
|
We are in the comfortable position of being left and right adjoint.
|
||||||
generation trivial cofibrations are pushout product of mono and endpoint inclusion into the interval.
|
\(i^*\) preserves the interval inclusion. As pushout products with the interval inclusion sends cofibrations
|
||||||
left and right adjoint functor (like \(i_*\) preserve these) pushout product with mono and interval
|
to trivial cofibrations and \(i^*\) preserves monomorphisms by \cref{prop:i*preservesMonos}, \(i^*\) sends trivial cofibrations
|
||||||
are also trivial cofibrations in \Δ.
|
to trivial cofibrations.
|
||||||
\end{proof}
|
\end{proof}
|
||||||
|
|
||||||
We get now to the difficult part of step \ref{step1}. The argument we are going to follow is due to Sattler
|
As the next proof is mostly a straight forward induction, we don't repeat the full argument and only give a proof sketch.
|
||||||
|
\begin{proposition}[{\cite[prop. 3.6]{sattlerIdempotentCompletionCubes2019}}]\label{prop:i!preservesTrivialCofib}
|
||||||
|
\(i_!\) preserves trivial cofibrations.
|
||||||
|
\end{proposition} \todo{\printline maybe give the full proof but low prio}
|
||||||
|
\begin{proof}[Proof sketch.]
|
||||||
|
It is fairly easy to see that \(i_!(\Yo -)\) on morphisms is valued in weak equivalences, by checking that representables in \dcSet are
|
||||||
|
weakly contractible.
|
||||||
|
Then one shows inductively that one can build the horn inclusions as pushouts of horn inclusion of dimension \(n\) and an
|
||||||
|
inclusion of the \(n\)-dimensional horn into a \(n+1\) dimensional horn. As \(i_!\) is cocontinuous and the trivial cofibrations
|
||||||
|
have as a left lifting class the necessary closure properties, the claim follows.
|
||||||
|
\end{proof}
|
||||||
|
|
||||||
|
We now get to the difficult part of step \ref{step1}. The argument we are going to follow is due to Sattler \cite{sattlerIdempotentCompletionCubes2019}
|
||||||
and involves the Reedy Structure of \(Δ\). We are going through the whole argument here, as it is a good preparation
|
and involves the Reedy Structure of \(Δ\). We are going through the whole argument here, as it is a good preparation
|
||||||
for \(j_!\) in step \ref{step2}.
|
for \(j_!\) in step \ref{step2}. We also use this to add a lot of detail and improve the criterion a bit, see the remark at \cref{lem:idemLemma3.5}.
|
||||||
\begin{proposition}[{\cite[prop. 3.3]{sattlerIdempotentCompletionCubes2019}}]
|
\begin{proposition}[{\cite[prop. 3.3]{sattlerIdempotentCompletionCubes2019}}]\label{prop:i!preservesMonos}
|
||||||
\(i_!\) preserves monomorphisms.
|
\(i_!\) preserves monomorphisms.
|
||||||
\end{proposition}
|
\end{proposition}
|
||||||
Following \cite{sattlerIdempotentCompletionCubes2019} we are first going to prove two technical lemma.
|
Following \cite{sattlerIdempotentCompletionCubes2019} we are first going to prove two technical lemmas.
|
||||||
Note that a repetition of this argument is also good to check if we actually need an elegant Reedy structure
|
Note that a repetition of this argument is also good to check if we actually need an elegant Reedy structure
|
||||||
or if we can do with just an Eilenberg-Zilber category.
|
or if we can do with just an Eilenberg-Zilber category.
|
||||||
|
|
||||||
|
@ -140,11 +162,11 @@ or if we can do with just an Eilenberg-Zilber category.
|
||||||
\end{lemma}
|
\end{lemma}
|
||||||
\begin{remark}
|
\begin{remark}
|
||||||
The original source has as an extra condition that these pullbacks preserve face and degeneracy maps. We
|
The original source has as an extra condition that these pullbacks preserve face and degeneracy maps. We
|
||||||
don't need this by making use of the fact that degeneracies split.
|
do not need this by making use of the fact that degeneracies split.
|
||||||
\end{remark}
|
\end{remark}
|
||||||
|
|
||||||
For this proof we will make some use of the equivalence between presheaves and discrete Grothendieck fibrations.
|
For this proof we will make some use of the equivalence between presheaves and discrete Grothendieck fibrations.
|
||||||
This has the benefit of exhibiting our monomorphism, as a Grothendieck fibration. We also can lift the
|
This has the benefit of exhibiting our monomorphism as a Grothendieck fibration. We also can lift the
|
||||||
Eilenberg-Zilber structure from our site, a notion that is hard to express with presheaves.
|
Eilenberg-Zilber structure from our site, a notion that is hard to express with presheaves.
|
||||||
|
|
||||||
\begin{lemma}\label{lem:liftEZFib}
|
\begin{lemma}\label{lem:liftEZFib}
|
||||||
|
@ -152,8 +174,8 @@ Eilenberg-Zilber structure from our site, a notion that is hard to express with
|
||||||
Then we can lift the Eilenberg-Zilber structure to \(Q\).
|
Then we can lift the Eilenberg-Zilber structure to \(Q\).
|
||||||
\end{lemma}
|
\end{lemma}
|
||||||
The hard part of the proof will be the lifting of absolute pushouts. In general pushouts don't need to
|
The hard part of the proof will be the lifting of absolute pushouts. In general pushouts don't need to
|
||||||
lift, as the fibre above the pushout in the base category might be empty. If we had a split pushout like in
|
lift, as the fiber above the pushout in the base category might be empty. If we had a split pushout like in
|
||||||
lemma \ref{absolutePushout}, we could lift the splits to solve that problem. Sadly not all absolute pushouts
|
\cref{absolutePushout}, we could lift the splits to solve that problem. Sadly, not all absolute pushouts
|
||||||
are of this form, but something a bit weaker is true. The first appearance of this observation seems to be
|
are of this form, but something a bit weaker is true. The first appearance of this observation seems to be
|
||||||
in \cite{pareAbsoluteColimits1971}.
|
in \cite{pareAbsoluteColimits1971}.
|
||||||
\begin{lemma}\label{lem:absPushChar}
|
\begin{lemma}\label{lem:absPushChar}
|
||||||
|
@ -165,9 +187,9 @@ in \cite{pareAbsoluteColimits1971}.
|
||||||
is an absolute pushout diagram if and only if there exists
|
is an absolute pushout diagram if and only if there exists
|
||||||
\begin{enumerate}
|
\begin{enumerate}
|
||||||
\item A section \(u : P → B\) of \(m\).
|
\item A section \(u : P → B\) of \(m\).
|
||||||
\item Morphisms \(r_1…r_k : B → A \) and \(s_1…s_k : B → A\) for some \( k ≥ 1\), such that \(ps_1 = \id_B\),
|
\item Morphisms \(r_1,…,r_k : B → A \) and \(s_1,…,s_k : B → A\) for some \( k ≥ 1\), such that \(ps_1 = \id_B\),
|
||||||
\(qs_i = qr_i\) for all \(i\), \(pr_i = ps_{i+1}\) for all \(i < k\), and \(pr_k = um\).
|
\(qs_i = qr_i\) for all \(i\), \(pr_i = ps_{i+1}\) for all \(i < k\), and \(pr_k = um\).
|
||||||
\item Morphisms \(t_1…t_{l+1} : C → A\) and \(v_1…v_l : C → A\) for some \(l ≥ 0\), such that \(qt_1 = \id_C\),
|
\item Morphisms \(t_1,…,t_{l+1} : C → A\) and \(v_1,…,v_l : C → A\) for some \(l ≥ 0\), such that \(qt_1 = \id_C\),
|
||||||
\(pt_i = pv_i\) for all \(i < l\), \(qv_i = qt_{i+1}\) for all \(i ≤ l\), and \(pt_{l+1} = un\).
|
\(pt_i = pv_i\) for all \(i < l\), \(qv_i = qt_{i+1}\) for all \(i ≤ l\), and \(pt_{l+1} = un\).
|
||||||
\end{enumerate}
|
\end{enumerate}
|
||||||
or the symmetric situation where \(B\) and \(C\) are interchanged.
|
or the symmetric situation where \(B\) and \(C\) are interchanged.
|
||||||
|
@ -178,7 +200,8 @@ in \cite{pareAbsoluteColimits1971}.
|
||||||
A \arrow[r, "p" ] \arrow[d, "q" ] & B \arrow[d, "b"] \\
|
A \arrow[r, "p" ] \arrow[d, "q" ] & B \arrow[d, "b"] \\
|
||||||
C \arrow[r, "c"] & X
|
C \arrow[r, "c"] & X
|
||||||
\end{eqcd*}
|
\end{eqcd*}
|
||||||
a commutative square. We now need to find a \(x : P → X\), that witnesses \(P\) as a pushout.
|
be a commutative square. As all this data gets preserved by any functor we only need to prove that such a diagram
|
||||||
|
is already a pushout. We now need to find a \(x : P → X\) that witnesses \(P\) as a pushout.
|
||||||
Since \(m\) splits, \(x\) will be unique automatically. We define \(x ≔ bu\). We now need to check
|
Since \(m\) splits, \(x\) will be unique automatically. We define \(x ≔ bu\). We now need to check
|
||||||
if it makes the both evident triangles commute. We do this by chasing though all the data we have been given.
|
if it makes the both evident triangles commute. We do this by chasing though all the data we have been given.
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
|
@ -186,29 +209,29 @@ in \cite{pareAbsoluteColimits1971}.
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
and
|
and
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
xn = bun = bpt_{l+1} = cqt_{l+1} = cqv_l = bpv_l = bpt_l = … = cqt_1 = c
|
xn = bun = bpt_{l+1} = cqt_{l+1} = cqv_l = bpv_l = bpt_l = … = cqt_1 = c \text{.}
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
|
|
||||||
Now let us assume the given square is an absolute pushout. Now we need to construct all the date from above.
|
Now let us assume the given square is an absolute pushout. Now we need to construct all the date from above.
|
||||||
To get the desired split \(u\), we will apply the \(hom(P,−)\) functor and get a pushout square in \(\Set\).
|
To get the desired split \(u\), we will apply the \(\Hom(P,−)\) functor and get a pushout square in \(\Set\).
|
||||||
\begin{eqcd*}
|
\begin{eqcd*}
|
||||||
\hom(P,A) \arrow[r, "p"] \arrow[d, "q"] \pu & \hom(P,B) \arrow[d, "m"] \\
|
\Hom(P,A) \arrow[r, "p"] \arrow[d, "q"] \pu & \Hom(P,B) \arrow[d, "m"] \\
|
||||||
\hom(P,C) \arrow[r, "n"] & \hom(P,P)
|
\Hom(P,C) \arrow[r, "n"] & \Hom(P,P)
|
||||||
\end{eqcd*}
|
\end{eqcd*}
|
||||||
That means we have a surjection from \(\hom(P,B) + \hom(P,C) → \hom(P,P)\).
|
That means we have a surjection from \(\Hom(P,B) + \Hom(P,C) → \Hom(P,P)\).
|
||||||
A preimage of \(\id_P\) under this surjection is a morphism \(u\) for that either \(mu = \id_P\)
|
A preimage of \(\id_P\) under this surjection is a morphism \(u\) for that either \(mu = \id_P\)
|
||||||
or \(nu = \id_P\) holds. We assume WLOG the first case.
|
or \(nu = \id_P\) holds. We assume WLOG the first case.
|
||||||
|
|
||||||
To get \(r_1…r_k\) and \(s_1…s_k\) that relate \(\id_B\) and \(um\), we look at the image under the
|
To get \(r_1,…,r_k\) and \(s_1,…,s_k\) that relate \(\id_B\) and \(um\), we look at the image under the
|
||||||
\(\hom(B,−)\) functor.
|
\(\Hom(B,−)\) functor.
|
||||||
\begin{eqcd*}
|
\begin{eqcd*}
|
||||||
\hom(B,A) \arrow[r, "p"] \arrow[d, "q"] \pu & \hom(B,B) \arrow[d, "m"] \\
|
\Hom(B,A) \arrow[r, "p"] \arrow[d, "q"] \pu & \Hom(B,B) \arrow[d, "m"] \\
|
||||||
\hom(B,C) \arrow[r, "n"] & \hom(B,P)
|
\Hom(B,C) \arrow[r, "n"] & \Hom(B,P)
|
||||||
\end{eqcd*}
|
\end{eqcd*}
|
||||||
We know that \(um\) and \(\id_B\), are getting sent to the same map in \(\hom(B,P)\), because
|
We know that \(um\) and \(\id_B\), are getting sent to the same map in \(\hom(B,P)\), because
|
||||||
\(mum = m = m\id_B\).
|
\(mum = m = m\id_B\).
|
||||||
We can now construct a sequence of maps in \(\hom(B,A)\) if we alternate between taking preimages of images
|
We can now construct a sequence of maps in \(\hom(B,A)\) if we alternate between taking preimages of images
|
||||||
under \(p\) and \(q\). Lets call the preimages along \(p\) \(s_i\), and the preimages along \(q\) \(r_i\).
|
under \(p\) and \(q\). Lets call the preimages along \(p\) by \(s_i\), and the preimages along \(q\) by \(r_i\).
|
||||||
This procedure immediately guarantees the equations
|
This procedure immediately guarantees the equations
|
||||||
\begin{align*}
|
\begin{align*}
|
||||||
qs_i = qr_i & & pr_i = ps_{i+1} \text{.}
|
qs_i = qr_i & & pr_i = ps_{i+1} \text{.}
|
||||||
|
@ -217,12 +240,12 @@ in \cite{pareAbsoluteColimits1971}.
|
||||||
\(um\) get sent to the same element along \(m\) there exists a \(k\) and a choice of \(r_i\) and \(s_i\) such that
|
\(um\) get sent to the same element along \(m\) there exists a \(k\) and a choice of \(r_i\) and \(s_i\) such that
|
||||||
\(pr_k = um\).
|
\(pr_k = um\).
|
||||||
|
|
||||||
The maps for condition three, can be constructed with the same technique after applying the \(\hom(C,−)\) functor.
|
The maps for condition three can be constructed with the same technique after applying the \(\hom(C,−)\) functor.
|
||||||
The index shift comes from the fact that \(\id_C ∈ \hom(C,C)\) and \(un ∈ \hom(C,B)\) are in opposite corners
|
The index shift comes from the fact that \(\id_C ∈ \hom(C,C)\) and \(un ∈ \hom(C,B)\) are in opposite corners
|
||||||
of the resulting diagram.
|
of the resulting diagram.
|
||||||
\end{proof}
|
\end{proof}
|
||||||
|
|
||||||
To be able to lift this structure make sure we can lift commuting triangles first.
|
To be able to lift this structure, we make sure we can lift commuting triangles first.
|
||||||
\begin{lemma}\label{lem:gfibliftcommute}
|
\begin{lemma}\label{lem:gfibliftcommute}
|
||||||
Let \(F : Q → \C\) be a discrete Grothendieck fibration, \(f: A → B\) be a morphism in \(Q\), and
|
Let \(F : Q → \C\) be a discrete Grothendieck fibration, \(f: A → B\) be a morphism in \(Q\), and
|
||||||
\(g : C → F(B)\) and \(h : F(A) → C\) such that \(gh = F(f)\). We can lift \(g\) and \(h\) to form
|
\(g : C → F(B)\) and \(h : F(A) → C\) such that \(gh = F(f)\). We can lift \(g\) and \(h\) to form
|
||||||
|
@ -238,7 +261,7 @@ To be able to lift this structure make sure we can lift commuting triangles firs
|
||||||
It also suffices to just give an object \(B\) and a commutative diagram in \C.
|
It also suffices to just give an object \(B\) and a commutative diagram in \C.
|
||||||
\end{remark}
|
\end{remark}
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
That we can get lifts \(g'\) and \(h'\) follows directly from the definition of discrete Grothendieck fibration.
|
That we can get lifts \(g'\) and \(h'\) follows directly from the definition of discrete Grothendieck fibrations.
|
||||||
We only need to argue that the domain of \(h'\) is indeed \(A\) and that the diagram commutes. As \(f\) and \(g'h'\) are lifts
|
We only need to argue that the domain of \(h'\) is indeed \(A\) and that the diagram commutes. As \(f\) and \(g'h'\) are lifts
|
||||||
of \(F(f) = gh\), we get \(f = g'h'\) by the uniqueness of lifts.
|
of \(F(f) = gh\), we get \(f = g'h'\) by the uniqueness of lifts.
|
||||||
\end{proof}
|
\end{proof}
|
||||||
|
@ -250,25 +273,25 @@ To be able to lift this structure make sure we can lift commuting triangles firs
|
||||||
these. Isomorphisms and split epis are preserved by every functor, so only noninvertible monomorphisms remain.
|
these. Isomorphisms and split epis are preserved by every functor, so only noninvertible monomorphisms remain.
|
||||||
We will establish this in two steps, first showing mono preservation and then reflection of inverses.
|
We will establish this in two steps, first showing mono preservation and then reflection of inverses.
|
||||||
|
|
||||||
Given some monomorphism \(f : A ↣B\) in \(Q\) and two morphisms \(g,h : C → \p(A)\) in \C, such that \(\p(f)h = \p(f)g \)
|
Given some monomorphism \(f : A ↣B\) in \(Q\) and two morphisms \(g,h : C → \p(A)\) in \C, such that \(\p(f)h = \p(f)g \),
|
||||||
We can lift \(g\) and \(h\) to \(g' : C' → A\) and \(h' : C' → A\). By lemma \ref{lem:gfibliftcommute} we have \(fg' = fh'\) and
|
we can lift \(g\) and \(h\) to \(g' : C' → A\) and \(h' : C' → A\). By \cref{lem:gfibliftcommute}, we have \(fg' = fh'\) and
|
||||||
thus \(g' = h'\). We get directly \( g = \p(g') = \p(h') = h\) and thus \(\p(f)\) is monic.
|
thus \(g' = h'\). We get directly \( g = \p(g') = \p(h') = h\) and thus \(\p(f)\) is monic.
|
||||||
|
|
||||||
Assume we have a map \(f\) in \(Q\) such that \(\p(f)\) has a (one sided) inverse. By lemma \ref{lem:gfibliftcommute} the lift
|
Assume we have a map \(f\) in \(Q\) such that \(\p(f)\) has a (one sided) inverse. By \cref{lem:gfibliftcommute}, the lift
|
||||||
of that (one sided) inverse, is also a (one sided) inverse of \(f\).
|
of that (one sided) inverse is also a (one sided) inverse of \(f\).
|
||||||
|
|
||||||
This fact also helps us directly in the next step. We need to show that every morphism factors into a split epi followed by
|
This fact also helps us directly in the next step. We need to show that every morphism factors into a split epi followed by
|
||||||
a monomorphism. We can lift a factorization by lemma \ref{lem:gfibliftcommute}, and as one sided inverses are preserved by lifting
|
a monomorphism. We can lift a factorization by \cref{lem:gfibliftcommute}, and as one sided inverses are preserved by lifting,
|
||||||
\(\p\) reflects split epis. So we only need to show that monos are preserved by liftings. Let \(f : A → B\) be a morphism
|
\(\p\) reflects split epis. So we only need to show that monos are preserved by liftings. Let \(f : A → B\) be a morphism
|
||||||
in \(Q\), such that \(\p(f)\) is monic and let \(g,h : C → A\) such that \(fg = fh\). Because \(p(f)\) is monic \(\p(g) = \p(h)\),
|
in \(Q\), such that \(\p(f)\) is monic and let \(g,h : C → A\) such that \(fg = fh\). Because \(p(f)\) is monic, \(\p(g) = \p(h)\),
|
||||||
and thus \(g\) and \(h\) are liftings of the same morphism. As liftings are unique \(g = h\) and \(f\) monic.
|
and thus \(g\) and \(h\) are liftings of the same morphism. As liftings are unique \(g = h\) and \(f\) is monic.
|
||||||
|
|
||||||
As a last step we must establish that a span of split epis has an absolute pushout. So let \(f: A → B \) and \(g : A → C\) be spilt
|
As a last step we must establish that a span of split epis has an absolute pushout. So let \(f: A → B \) and \(g : A → C\) be spilt
|
||||||
epimorphisms in \(Q\). As these are preserved by functors \(\p(f)\) and \(\p(g)\) are split epis too. So there is an absolute pushout
|
epimorphisms in \(Q\). As these are preserved by functors, \(\p(f)\) and \(\p(g)\) are split epis too. So there is an absolute pushout
|
||||||
of \(\p(f)\) and \(\p(g)\). By lemma \ref{lem:absPushChar}, we can extend this square, by all the extra morphisms that characterize
|
of \(\p(f)\) and \(\p(g)\). By \cref{lem:absPushChar}, we can extend this square, by all the extra morphisms that characterize
|
||||||
the absolute pushout. We first lift the split established by 1 in lemma \ref{lem:absPushChar}, to get our candidate pushout.
|
the absolute pushout. We first lift the split established by 1. in \cref{lem:absPushChar}, to get our candidate pushout.
|
||||||
Lifting the rest of the data, and checking that the required equalities still hold is a tedious but straight forward repeated
|
Lifting the rest of the data and checking that the required equalities still hold is a tedious but straight forward repeated
|
||||||
application of lemma \ref{lem:liftEZFib}. Afterwards we can apply lemma \ref{lem:absPushChar} again to verify that we indeed got
|
application of \cref{lem:liftEZFib}. Afterwards we can apply \cref{lem:absPushChar} again to verify that we indeed got
|
||||||
an absolute pushout in \(Q\).
|
an absolute pushout in \(Q\).
|
||||||
\end{proof}
|
\end{proof}
|
||||||
\begin{remark}
|
\begin{remark}
|
||||||
|
@ -279,12 +302,12 @@ To be able to lift this structure make sure we can lift commuting triangles firs
|
||||||
\end{remark}
|
\end{remark}
|
||||||
|
|
||||||
\begin{lemma}\label{lem:liftPullbacks}
|
\begin{lemma}\label{lem:liftPullbacks}
|
||||||
Let \(F : Q → \C\) be a discrete Grothendieck fibration. Given as span in \(Q\) and a pullback of the image of the
|
Let \(F : Q → \C\) be a discrete Grothendieck fibration. Given a span in \(Q\) and a pullback of the image of the
|
||||||
span in \C. Then there exists a lift of that pullback completing the original span to a pullback square.
|
span in \C, then there exists a lift of that pullback completing the original span to a pullback square.
|
||||||
\end{lemma}
|
\end{lemma}
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
Let \(p : A → C\) and \(q : B → C\) be a span in \(Q\), such that its image under \(F\) completes to a pullback
|
Let \(p : A → C\) and \(q : B → C\) be a span in \(Q\), such that its image under \(F\) completes to a pullback
|
||||||
square. We can lift this square to a commuting square in \(Q\), by lemma \ref{lem:gfibliftcommute}.
|
square. We can lift this square to a commuting square in \(Q\) by \cref{lem:gfibliftcommute}.
|
||||||
We now need to check that this again a pullback square.
|
We now need to check that this again a pullback square.
|
||||||
\begin{eqcd*}[column sep=tiny, row sep=small]
|
\begin{eqcd*}[column sep=tiny, row sep=small]
|
||||||
X \arrow[dd, bend right, "x"' ] \arrow[rrrd, bend left=15, "y"] \arrow[dr, dashed] & & & \\
|
X \arrow[dd, bend right, "x"' ] \arrow[rrrd, bend left=15, "y"] \arrow[dr, dashed] & & & \\
|
||||||
|
@ -294,27 +317,27 @@ To be able to lift this structure make sure we can lift commuting triangles firs
|
||||||
& P \arrow[rr,"p"] \arrow[dl,"q"'] \pb & & F(A) \arrow[dl,"F(f)"] \\
|
& P \arrow[rr,"p"] \arrow[dl,"q"'] \pb & & F(A) \arrow[dl,"F(f)"] \\
|
||||||
F(B) \arrow[rr, "F(g)"'] & & F(C) &
|
F(B) \arrow[rr, "F(g)"'] & & F(C) &
|
||||||
\end{eqcd*}
|
\end{eqcd*}
|
||||||
So let us take any cospan \((x,y)\) that completes the span \((f,g)\) to a commuting square in \(Q\).
|
So let us take any span \((x,y)\) that completes the cospan \((f,g)\) to a commuting square in \(Q\).
|
||||||
We can map this to \C via \(F\) and get a universal map witnessing that the square in \C is indeed a pullback.
|
We can map this to \C via \(F\) and get a universal map witnessing that the square in \C is indeed a pullback.
|
||||||
We can lift this map uniquely to \(P'\) along \(F\), and by lemma \ref{lem:gfibliftcommute} this lift makes the
|
We can lift this map uniquely to \(P'\) along \(F\), and by lemma \ref{lem:gfibliftcommute} this lift makes the
|
||||||
diagram commute.
|
diagram commute.
|
||||||
\end{proof}
|
\end{proof}
|
||||||
|
|
||||||
We will also need another technical property of discrete Grothendieck fibrations and Eilenberg-Zilber categories.
|
% We will also need another technical property of discrete Grothendieck fibrations and Eilenberg-Zilber categories.
|
||||||
\begin{lemma}\label{lem:bifib}
|
% \begin{lemma}\label{lem:bifib}
|
||||||
Let \(F : P ↣ \C\) be a a monic discrete Grothendieck fibration, and \C be an Eilenberg-Zilber (or elegant Reedy) category. Then
|
% Let \(F : P ↣ \C\) be a a monic discrete Grothendieck fibration, and \C be an Eilenberg-Zilber (or elegant Reedy) category. Then
|
||||||
\(F\) as opcartesian lifts of degeneracy maps. \todo{check if we introduced “degeneracy” and “face” as words in the definition}
|
% \(F\) as opcartesian lifts of degeneracy maps. \todo{\printline check if we introduced “degeneracy” and “face” as words in the definition}
|
||||||
\end{lemma}
|
% \end{lemma}
|
||||||
\begin{proof}
|
% \begin{proof}
|
||||||
So let \(A\) be an object in P and \(f : F(A) → B\) be a degeneracy in \C i.e. a split epi.
|
% So let \(A\) be an object in P and \(f : F(A) → B\) be a degeneracy in \C i.e. a split epi.
|
||||||
We can then lift the split to \(A\), and get a morphism \(g : B' → A\) where \(B'\) is the unique object
|
% We can then lift the split to \(A\), and get a morphism \(g : B' → A\) where \(B'\) is the unique object
|
||||||
above \(B\). We can now lift \(f\), to \(B'\) and get a morphism \(f': A → B'\) above \(f\). Verifying that
|
% above \(B\). We can now lift \(f\), to \(B'\) and get a morphism \(f': A → B'\) above \(f\). Verifying that
|
||||||
\(f'\) has the required universal property is a straight forward repeated application of lemma \ref{lem:gfibliftcommute}.
|
% \(f'\) has the required universal property is a straight forward repeated application of lemma \ref{lem:gfibliftcommute}.
|
||||||
\end{proof}
|
% \end{proof}
|
||||||
|
|
||||||
\begin{proof}[Proof of Lemma \ref{lem:idemLemma3.4}]
|
\begin{proof}[Proof of Lemma \ref{lem:idemLemma3.4}]
|
||||||
Let \(f : P' ↣ Q'\) be a monomorphism in \(\hat{\C}\). This gives equivalently rise to a monomorphism \(F\)
|
Let \(f : P' ↣ Q'\) be a monomorphism in \(\hat{\C}\). This gives equivalently rise to a monomorphism \(F\)
|
||||||
of discrete Grothendieck fibrations via the category of elements. \todo{do I need to explain this?}
|
of discrete Grothendieck fibrations via the category of elements.
|
||||||
We define \(P ≔ \int P'\), \(Q ≔ \int Q'\) and \(F ≔ \int f\).
|
We define \(P ≔ \int P'\), \(Q ≔ \int Q'\) and \(F ≔ \int f\).
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
\begin{tikzcd}[column sep=tiny, row sep=small]
|
\begin{tikzcd}[column sep=tiny, row sep=small]
|
||||||
|
@ -323,22 +346,20 @@ We will also need another technical property of discrete Grothendieck fibrations
|
||||||
\end{tikzcd}
|
\end{tikzcd}
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
That \(\colim\) sends \(f\) to a monomorphism,
|
That \(\colim\) sends \(f\) to a monomorphism,
|
||||||
can equivalently stated that \(F\) is monic on connected components. That follows directly from the explicit construction
|
is equivalent to the statement that \(F\) is monic on connected components. That follows directly from the explicit construction
|
||||||
of colimits in \(\Set\). Also \(F\) gets to be a discrete Grothendieck fibration on its own. We can lift the Eilenberg-Zilber
|
of colimits in \(\Set\). Also \(F\) gets to be a discrete Grothendieck fibration on its own. We can lift the Eilenberg-Zilber
|
||||||
structure to \(Q\) by lemma \ref{lem:liftEZFib}. Also \(F\) is a bifibration if restricted to the degeneracy maps by lemma \ref{lem:bifib}.
|
structure to \(Q\) by \cref{lem:liftEZFib}.
|
||||||
\todo{We don't need this (and the lemma) anymore}
|
|
||||||
|
|
||||||
So now let S and T be be objects of \(P\) such that \(F(S)\) and \(F(T)\) lie in the same connected component of \(Q\).
|
So now let \(S\) and \(T\) be be objects of \(P\) such that \(F(S)\) and \(F(T)\) lie in the same connected component of \(Q\).
|
||||||
This means there is a zigzag connecting \(F(S)\) and \(F(T)\). We can normalize this to a span. To see this we are going
|
This means there is a zigzag connecting \(F(S)\) and \(F(T)\). We can normalize this to a span. To see this, we are going
|
||||||
to show how to turn a cospan into a span of morphisms. So let \( f : D → B\) and \( g : E → B \) be a cospan. Because of the Eilenberg-Zilber
|
to show how to turn a cospan into a span of morphisms. So let \( f : D → B\) and \( g : E → B \) be a cospan. Because of the Eilenberg-Zilber
|
||||||
structure we can factor those into a degeneracy followed by a face map. Lets call them \(f_d\), \(f_f\), \(g_d\) and \(g_f\).
|
structure, we can factor those into a degeneracy followed by a face map. Lets call them \(f_d\), \(f_f\), \(g_d\) and \(g_f\).
|
||||||
\todo{lift the pullback property}
|
|
||||||
\begin{eqcd*}[column sep=small]
|
\begin{eqcd*}[column sep=small]
|
||||||
D \arrow[dr, two heads, "f_d"] & & P \arrow [dr, tail] \arrow[dl, tail] \arrow[dd, phantom,very near start, "\rotatebox{-45}{\(\lrcorner\)}"]& & E \arrow[dl, two heads, "g_d"'] \\
|
D \arrow[dr, two heads, "f_d"] & & P \arrow [dr, tail] \arrow[dl, tail] \arrow[dd, phantom,very near start, "\rotatebox{-45}{\(\lrcorner\)}"]& & E \arrow[dl, two heads, "g_d"'] \\
|
||||||
{} & • \arrow[dr, tail, "f_f"] \arrow[lu, bend left] & & • \arrow[dl,tail, "g_f"'] \arrow[ru, bend right] & \\
|
{} & • \arrow[dr, tail, "f_f"] \arrow[lu, bend left] & & • \arrow[dl,tail, "g_f"'] \arrow[ru, bend right] & \\
|
||||||
{} & & B & &
|
{} & & B & &
|
||||||
\end{eqcd*}
|
\end{eqcd*}
|
||||||
We can then construct the pullback \(P\) along \(f_f\) and \(g_f\), and the resulting maps concated with the splits of \(f_d\) and \(g_d\)
|
We can then construct the pullback \(P\) along \(f_f\) and \(g_f\), and the resulting maps concatenated with the splits of \(f_d\) and \(g_d\)
|
||||||
are a span over \(D\) and \(E\). This means \(F(S)\) and \(F(T)\) are connected by a span of morphisms. Because \(F\) is injective
|
are a span over \(D\) and \(E\). This means \(F(S)\) and \(F(T)\) are connected by a span of morphisms. Because \(F\) is injective
|
||||||
on objects we can lift this span to a span from \(S\) to \(T\) and thus \(S\) and \(T\) are in the same connected component.
|
on objects we can lift this span to a span from \(S\) to \(T\) and thus \(S\) and \(T\) are in the same connected component.
|
||||||
\end{proof}
|
\end{proof}
|
||||||
|
@ -349,16 +370,16 @@ structures. Sadly this does not work well for Eilenberg-Zilber categories. So we
|
||||||
\begin{lemma}\label{liftReedyToComma}
|
\begin{lemma}\label{liftReedyToComma}
|
||||||
Let \A be an elegant Reedy category, \(i : \A → \B \) a functor and \(B ∈ \B \) an object in \B. We can lift
|
Let \A be an elegant Reedy category, \(i : \A → \B \) a functor and \(B ∈ \B \) an object in \B. We can lift
|
||||||
the elegant Reedy structure along \(p : B ↓ i → \A \), where \(p\) is the evident projection from the comma
|
the elegant Reedy structure along \(p : B ↓ i → \A \), where \(p\) is the evident projection from the comma
|
||||||
category. \todo{fill the gaps}
|
category.
|
||||||
\end{lemma}
|
\end{lemma}
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
First we need to define a degree function \(\d: \Obj (\B) → ℕ\), let \(\d'\) be the degree function from the elegant Reedy structure
|
First we need to define a degree function \(\d: \Obj (\B) → ℕ\), let \(\d'\) be the degree function from the elegant Reedy structure
|
||||||
we can then define \(\d ≔ \d'p\). We define the degeneracies and faces, as being degeneracies and faces under \(p\).
|
we can then define \(\d ≔ \d'p\). We define the degeneracies and faces, as being degeneracies and faces under \(p\).
|
||||||
Here we would already get a problem with EZ-categories as we might have maps that are monic in \(B ↓ i\), but not in \B.
|
Here we would already get a problem with EZ-categories as we might have maps that are monic in \(B ↓ i\), but not in \B.
|
||||||
|
|
||||||
As a next step we need to construct desired factorization into a degeneracy and a face map. So we take
|
As a next step we need to construct the desired factorization into a degeneracy and a face map. So we take
|
||||||
a map \(f\) in \(B ↓ i\) and factor it as a map in \A into \(f = f_f f_d\). If we try to lift the factorization
|
a map \(f\) in \(B ↓ i\) and factor it as a map in \A into \(f = f_f f_d\). If we try to lift the factorization
|
||||||
we end up with the following diagram.
|
we end up with the following diagram:
|
||||||
\begin{eqcd*}
|
\begin{eqcd*}
|
||||||
{} & B \arrow[dl, "ϕ"'] \arrow[dr, "ϕ'"] & \\
|
{} & B \arrow[dl, "ϕ"'] \arrow[dr, "ϕ'"] & \\
|
||||||
i(A) \arrow[rr,"i(f)", near start] \arrow[dr, "i(f_d)"'] & & i(A') \\
|
i(A) \arrow[rr,"i(f)", near start] \arrow[dr, "i(f_d)"'] & & i(A') \\
|
||||||
|
@ -381,14 +402,14 @@ structures. Sadly this does not work well for Eilenberg-Zilber categories. So we
|
||||||
\end{remark}
|
\end{remark}
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
So consider a span of maps in \(B ↓ i\). That fulfills the conditions of this lemma.
|
So consider a span of maps in \(B ↓ i\). That fulfills the conditions of this lemma.
|
||||||
If we unravel this, we get the following diagram
|
If we unravel this, we get the following diagram:
|
||||||
\begin{eqcd*}
|
\begin{eqcd*}
|
||||||
{} & B \arrow[rdd, "ϕ'", bend left] \arrow[ldd, "ϕ"', bend right] & \\
|
{} & B \arrow[rdd, "ϕ'", bend left] \arrow[ldd, "ϕ"', bend right] & \\
|
||||||
{} & & \\
|
{} & & \\
|
||||||
i(X) \arrow[rd, "i(f)"] & & i(Y) \arrow[ld, "i(g)"'] \\
|
i(X) \arrow[rd, "i(f)"] & & i(Y) \arrow[ld, "i(g)"'] \\
|
||||||
{} & i(Z) &
|
{} & i(Z) &
|
||||||
\end{eqcd*}
|
\end{eqcd*}
|
||||||
By assumption we have pullbacks of \(i(f)\) and \(i(g)\) in \B, that lies in the image of \(i\). So we
|
By assumption we have pullbacks of \(i(f)\) and \(i(g)\) in \B that lie in the image of \(i\). So we
|
||||||
can complete the diagram
|
can complete the diagram
|
||||||
\begin{eqcd*}
|
\begin{eqcd*}
|
||||||
{} & B \arrow[rdd, "ϕ'", bend left] \arrow[ldd, "ϕ"', bend right] \arrow[d,dashed, "{⟨ϕ,ϕ'⟩}"] & \\
|
{} & B \arrow[rdd, "ϕ'", bend left] \arrow[ldd, "ϕ"', bend right] \arrow[d,dashed, "{⟨ϕ,ϕ'⟩}"] & \\
|
||||||
|
@ -406,124 +427,132 @@ structures. Sadly this does not work well for Eilenberg-Zilber categories. So we
|
||||||
\end{lemma}
|
\end{lemma}
|
||||||
\begin{remark}
|
\begin{remark}
|
||||||
The original source also requires that these pullbacks preserve face and degeneracy maps. We get around this by making use of the fact
|
The original source also requires that these pullbacks preserve face and degeneracy maps. We get around this by making use of the fact
|
||||||
that degeneracies are split in lemma \ref{lem:liftEZFib}
|
that degeneracies are split in \cref{lem:liftEZFib}.
|
||||||
\end{remark}
|
\end{remark}
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
We only need to show that \(i_!\) preserves monomorphisms component wise, giving us a functor from \(\hat{\A} → \Set\) for every
|
We only need to show that \(i_!\) preserves monomorphisms component wise, giving us a functor from \(\hat{\A} → \Set\) for every
|
||||||
object in \( B ∈\B\). This functor can be written as \todo{argue why stacks project 00VC}
|
object in \( B ∈\B\). This functor can be written as
|
||||||
\begin{eqcd*}
|
\begin{eqcd*}
|
||||||
\hat{\A} \arrow[r,"p^*"] & \widehat{B ↓ i} \arrow[r,"\colim"] & \Set
|
\hat{\A} \arrow[r,"p^*"] & \widehat{B ↓ i} \arrow[r,"\colim"] & \Set
|
||||||
\end{eqcd*}
|
\end{eqcd*}
|
||||||
where \(p : B ↓ i → \A\) is the projection.
|
where \(p : B ↓ i → \A\) is the projection.
|
||||||
This is the usual construction of \(i_!\) in this setting, see for example \cite{stacks00VC}.
|
This is the usual construction of \(i_!\) in this setting, see for example \cite{stacks00VC}.
|
||||||
It is trivial that \(p^*\) preserves monomorphisms, so we only need to check that \(\colim\) does.
|
It is trivial that \(p^*\) preserves monomorphisms, so we only need to check that \(\colim\) does.
|
||||||
We want to apply lemma \ref{lem:idemLemma3.4}
|
We want to apply \cref{lem:idemLemma3.4}.
|
||||||
We can lift the elegant Reedy structure from \A to \( B ↓ i \) along \(p\) by lemma \ref{liftReedyToComma}.
|
We can lift the elegant Reedy structure from \A to \( B ↓ i \) along \(p\) by \cref{liftReedyToComma}.
|
||||||
And as the face maps in \(B↓i\) are defined as maps that \(p\) sends to face maps in \A. We can lift the
|
And as the face maps in \(B↓i\) are defined as maps that \(p\) sends to face maps in \A. We can lift the
|
||||||
required pullbacks to \(B↓i\) by lemma \ref{commaPullback}.
|
required pullbacks to \(B↓i\) by \cref{commaPullback}.
|
||||||
\end{proof}
|
\end{proof}
|
||||||
\begin{proposition}[{\cite[proposition 3.3]{sattlerIdempotentCompletionCubes2019}}]\label{idemProp3.3}
|
|
||||||
\(i_! : \hat{Δ} → \widehat{□_{∧∨}}\) preserves monomorphisms.
|
|
||||||
\end{proposition}
|
\begin{proof}[Proof of \cref{prop:i!preservesMonos}]
|
||||||
\begin{proof}
|
We want to verify the conditions for \cref{lem:idemLemma3.5}. Our first observation is that \(Δ\) does not have arbitrary
|
||||||
We want to verify the conditions for lemma \ref{lem:idemLemma3.5}. Our first observation is, that \(Δ\). Dos not have arbitrary
|
pullbacks of face maps. Intuitively speaking we have only the non-empty ones. So let us unpack the condition that
|
||||||
pullbacks of face maps. Intuitively speaking we have only the non empty ones. So let us unpack the condition that
|
|
||||||
we only need pullbacks if the cospan of face maps lies in the image of the projection \(B ↓ i → Δ\) for some \(B\).
|
we only need pullbacks if the cospan of face maps lies in the image of the projection \(B ↓ i → Δ\) for some \(B\).
|
||||||
That means there is a \(B ∈ \FL\) such that
|
That means there is a \(B ∈ \FL\) such that the following square commutes:
|
||||||
\begin{eqcd*}
|
\begin{eqcd*}
|
||||||
{} & B \arrow[rd] \arrow[ld] & \\
|
{} & B \arrow[rd] \arrow[ld] & \\
|
||||||
i(X) \arrow[rd, "i(f_f)"] & & i(Y) \arrow[ld, "i(g_f)"'] \\
|
i(X) \arrow[rd, "i(f_f)"] & & i(Y) \arrow[ld, "i(g_f)"'] \\
|
||||||
{} & i(Z) &
|
{} & i(Z) &
|
||||||
\end{eqcd*}
|
\end{eqcd*} %COMMENT
|
||||||
As the face maps in \(Δ\) are monic we can identify \(X\) and \(Y\) with their respective image in \(Z\). As \FL does not
|
As the face maps in \(Δ\) are monic, we can identify \(X\) and \(Y\) with their respective image in \(Z\). As \FL does not
|
||||||
contain the empty poset, they share at least a point, and the pullback is given by \(\im f_f ∩ \im g_f\). A quick calculation
|
contain the empty poset, they share at least a point, and the pullback is given by \(\im f_f ∩ \im g_f\). A quick calculation
|
||||||
shows that this is also a pullback in \FL and thus we can apply lemma \ref{lem:idemLemma3.5}
|
shows that this is also a pullback in \FL and thus we can apply \cref{lem:idemLemma3.5}
|
||||||
\end{proof}
|
\end{proof}
|
||||||
|
|
||||||
|
|
||||||
\subsection{Step 2}
|
\subsection{\(j^*\) and \(j_!\) are left Quillen}
|
||||||
We are now going to show that \(j^*\) and \(j_!\) are left Quillen. As expected the hard part will be again to show that
|
We are now going to show that \(j^*\) and \(j_!\) are left Quillen. As expected, the hard part will be again to show that
|
||||||
\(j_!\) preserves monomorphisms.
|
\(j_!\) preserves monomorphisms.
|
||||||
|
|
||||||
So let us start with \(j^*\) again.
|
So let us start with \(j^*\) again.
|
||||||
|
|
||||||
\begin{proposition}
|
\begin{proposition}\label{prop:j*preservesMonos}
|
||||||
\(j^*\) preserves monomorphisms.
|
\(j^*\) preserves monomorphisms.
|
||||||
\end{proposition}
|
\end{proposition}
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
t \todo{trivial}
|
Follows directly from \cref{lem:restrictionPreserveMonos}
|
||||||
\end{proof}
|
\end{proof}
|
||||||
|
|
||||||
\begin{proposition}
|
\begin{proposition}\label{prop:j^*preservesTrivialCofib}
|
||||||
\(j^*\) preserves trivial cofibration
|
\(j^*\) preserves trivial cofibrations.
|
||||||
\end{proposition}
|
\end{proposition}
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
t \todo{same as \(i^*\)}
|
Like in \cref{prop:i*preservesTrivialCofib}, we are in the comfortable position of being left and right adjoint.
|
||||||
|
Note that \(j^*\) also preserves the interval inclusion. As pushout products with the interval inclusion send cofibrations
|
||||||
|
to trivial cofibrations and \(j^*\) preserves monomorphisms by \cref{prop:j*preservesMonos}, \(j^*\) sends trivial cofibrations
|
||||||
|
to trivial cofibrations.
|
||||||
\end{proof}
|
\end{proof}
|
||||||
|
|
||||||
\begin{proposition}
|
\begin{proposition}\label{prop:j!preservesTrivialCofib}
|
||||||
\(j^*\) preserves fibrations (bäh)
|
\(j^*\) preserves fibrations
|
||||||
\end{proposition}
|
\end{proposition}
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
t \todo{do i really need todo this?}
|
Preservation of uniform fibrations is clear, as every lifting problem against a generating trivial cofibration factors
|
||||||
\end{proof}
|
throug the image of a trivial cofibration under \(j^*\). As \(j^*\) preserves coequalizer the equivariance follows
|
||||||
|
from the equivariance of the model category on \dcSet, which follows from the presence of (at least one connection).
|
||||||
|
\end{proof}\todo{define uniform fibrations without equivariance}\todo{make a lemma that \dcSet is equivariant even if we just cite this from the relative elegance paper}
|
||||||
|
|
||||||
We want to recap the general proof idea, that \(i_!\) preserved monos. We can test being a monomorphism component wise and can write the
|
We want to recap the general proof idea that \(i_!\) preserved monos. We can test being a monomorphism component wise and can write the
|
||||||
left Kan extension evaluated at a point as some mono preserving functor followed by a colimit.
|
left Kan extension evaluated at a point as some mono preserving functor followed by a colimit.
|
||||||
That the colimit preserves monomorphisms is equivalent to a condition of connected on the categories
|
That the colimit preserves monomorphisms is equivalent to a condition of connected components on the categories
|
||||||
of elements. As we can only lift morphisms backwards along discrete Grothendieck fibrations, but we are faced
|
of elements. We can only lift morphisms backwards along discrete Grothendieck fibrations, but we are faced
|
||||||
with zigzags. To remedy this we want to lift a strong enough pullback property to turn these zigzags into spans.
|
with zigzags. To remedy this we want to lift a strong enough pullback property to turn these zigzags into spans.
|
||||||
|
|
||||||
This strategy will be the same \(j_!\). Sadly we couldn't get arbitrary Eilenberg-Zilber structures to lift, so
|
This strategy will be the same for \(j_!\). Sadly we couldn't get arbitrary Eilenberg-Zilber structures to lift, so
|
||||||
we will need a slightly different attack point.
|
we will need a slightly different attack point.
|
||||||
|
|
||||||
We first observe that \(□\) has a lot more pullbacks then \(Δ\). While \(Δ\) has only “non empty” pullbacks of face maps
|
We first observe that \(□\) has a lot more pullbacks then \(Δ\). While \(Δ\) has only “non-empty” pullbacks of face maps,
|
||||||
\(□\) has all “non empty" pullbacks. This elevates us from the necessity to lift the Eilenberg-Zilber structure to \(B ↓ i\).
|
\(□\) has all “non-empty" pullbacks. This elevates us from the necessity to lift the Eilenberg-Zilber structure to \(B ↓ i\).
|
||||||
We can get by with the following lemma.
|
We can get by with the following lemma.
|
||||||
|
|
||||||
\begin{lemma}\label{lem:pullbackMono}
|
\begin{lemma}\label{lem:pullbackMono}
|
||||||
Let \(i: \A → \B\) be a functor, such that for all \(B ∈ \B\), spans in the image of the projection \(p: B ↓ i\) have pullbacks
|
Let \(i: \A → \B\) be a functor such that for all \(B ∈ \B\), spans in the image of the projection \(p: B ↓ i\) have pullbacks
|
||||||
in \B, and these pullbacks are in the image of \(i\). Then \(i_!\) preserves monomorphisms.
|
in \B, and these pullbacks are in the image of \(i\). Then \(i_!\) preserves monomorphisms.
|
||||||
\end{lemma}
|
\end{lemma}
|
||||||
|
|
||||||
To show this we replace lemma \ref{lem:idemLemma3.4} with the following simpler lemma.
|
To show this we replace \cref{lem:idemLemma3.4} with the following simpler lemma.
|
||||||
|
|
||||||
\begin{lemma}\label{lem:colimPullbackMono}
|
\begin{lemma}\label{lem:colimPullbackMono}
|
||||||
Let \C be a category. Assume \C has pullbacks, then the functor \(\colim : \hat{\C} → \Set\) preserves monomorphisms.
|
Let \C be a category. Assume \C has pullbacks, then the functor \(\colim : \hat{\C} → \Set\) preserves monomorphisms.
|
||||||
\end{lemma}
|
\end{lemma}
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
Again let \(f\) be a monomorphism in \(\hat{\C}\). This is equivalently a monomorphism \(F: P → Q\) of discrete Grothendieck fibrations
|
Again let \(f\) be a monomorphism in \(\hat{\C}\). This is equivalently a monomorphism \(F: P → Q\) of discrete Grothendieck fibrations
|
||||||
over \C. We need to show that \(F\) is injective on connected components. We can lift the pullbacks to \(Q\) by lemma \ref{lem:liftPullbacks}.
|
over \C. We need to show that \(F\) is injective on connected components. We can lift the pullbacks to \(Q\) by \cref{lem:liftPullbacks}.
|
||||||
Let now \(S\) and \(T\) be in \(Q\) such that \(F(S)\) and \(F(T)\) are connected by a zigzag. We can turn this zigzag into a span, by
|
Let now \(S\) and \(T\) be in \(Q\) such that \(F(S)\) and \(F(T)\) are connected by a zigzag. We can turn this zigzag into a span, by
|
||||||
taking pullbacks of cospans. Because \(F\) is monic it is injective on object and we can lift this span to a span in \(P\) and thus
|
taking pullbacks of cospans. Because \(F\) is monic it is injective on objects and we can lift this span to a span in \(P\) and thus
|
||||||
\(S\) and \(T\) are in the same connected component.
|
\(S\) and \(T\) are in the same connected component.
|
||||||
\end{proof}
|
\end{proof}
|
||||||
|
|
||||||
\begin{proof}[Proof of lemma \ref{lem:pullbackMono}]
|
\begin{proof}[Proof of \cref{lem:pullbackMono}]
|
||||||
As in lemma \ref{lem:idemLemma3.5}, we check that \(i_!\) preserves monos component wise. We write \(i_!(B)\) again as
|
As in \cref{lem:idemLemma3.5}, we check that \(i_!\) preserves monos component wise. We write \(i_!(B)\) again as
|
||||||
\begin{eqcd*}
|
\begin{eqcd*}
|
||||||
\hat{\A} \arrow[r, "p^*"] & \widehat{B ↓ i} \arrow[r, "\colim"] & \Set
|
\hat{\A} \arrow[r, "p^*"] & \widehat{B ↓ i} \arrow[r, "\colim"] & \Set
|
||||||
\end{eqcd*}
|
\end{eqcd*}
|
||||||
where \(p : B ↓ i → A\) is the projection map. We need to show that \(B ↓ i\) has pullbacks, but that is an immediate
|
where \(p : B ↓ i → A\) is the projection map. We need to show that \(B ↓ i\) has pullbacks, but that is an immediate
|
||||||
consequence of lemma \ref{commaPullback}.
|
consequence of \cref{commaPullback}.
|
||||||
\end{proof}
|
\end{proof}
|
||||||
|
|
||||||
And we arrive at the conclusion we wanted to get to:
|
And we arrive at the conclusion we wanted to get to:
|
||||||
\begin{proposition}
|
\begin{lemma}
|
||||||
|
Let \(F: \A → \B\) be a functor, then the restriction functor \(F^* : \hat{\B} → \hat{\A}\) preserves monomorphisms.
|
||||||
|
\end{lemma}
|
||||||
|
|
||||||
|
\begin{proposition}\label{prop:j!preservesMonos}
|
||||||
\(j_! : \widehat{\FL} → \□\) preserves monomorphisms.
|
\(j_! : \widehat{\FL} → \□\) preserves monomorphisms.
|
||||||
\end{proposition}
|
\end{proposition}
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
For this proof we will identify \(2 = \{⊥,⊤\}\).
|
For this proof we will identify \(2 = \{⊥,⊤\}\).
|
||||||
We want to fulfill the conditions of \fref{lem:pullbackMono}. To check these conditions we check that equalizer and products
|
We want to fulfill the conditions of \cref{lem:pullbackMono}. To check these conditions, we check that equalizers and products
|
||||||
with the desired conditions exist. Products are a straightforward calculation so we go forward to the equalizer case.
|
with the desired conditions exist. Products are a straightforward calculation so we go forward to the equalizer case.
|
||||||
To check this we will look at a diagram of the following form.
|
To check this we will look at a diagram of the following form,
|
||||||
\begin{eqcd*}[column sep=small]
|
\begin{eqcd*}[column sep=small]
|
||||||
{} & B \arrow[ld] \arrow[rd] & \\
|
{} & B \arrow[ld] \arrow[rd] & \\
|
||||||
𝟚^n \arrow[rr, "j(f)", shift left] \arrow[rr, "j(g)"', shift right] & & 𝟚^m
|
𝟚^n \arrow[rr, "j(f)", shift left] \arrow[rr, "j(g)"', shift right] & & 𝟚^m
|
||||||
\end{eqcd*}
|
\end{eqcd*}
|
||||||
where we identify \(f\) and \(g\) with functions \(m → n + 2\).
|
where we identify \(f\) and \(g\) with functions \(m → n + 2\).
|
||||||
We note that equalizer, if they exist in \FL, are constructed the same way as in \Set.
|
We note that equalizers, if they exist in \FL, are constructed the same way as in \Set.
|
||||||
If we apply this to our diagram we can see, that this construction can't create something empty,
|
If we apply this to our diagram, we can see that this construction can't create something empty,
|
||||||
as both maps needs to preserve elements from \(B\).
|
as both maps needs to preserve elements from \(B\).
|
||||||
We would like to complete the diagram in the following way
|
We would like to complete the diagram in the following way
|
||||||
%\begin{eqcd*}[column sep=large]
|
%\begin{eqcd*}[column sep=large]
|
||||||
|
@ -533,9 +562,9 @@ And we arrive at the conclusion we wanted to get to:
|
||||||
𝟚^l \arrow[r,"j(e)"] & 𝟚^n \arrow[r,"j(f)", shift left] \arrow[r,"j(g)"',shift right] & 𝟚^m
|
𝟚^l \arrow[r,"j(e)"] & 𝟚^n \arrow[r,"j(f)", shift left] \arrow[r,"j(g)"',shift right] & 𝟚^m
|
||||||
\end{tikzcd}
|
\end{tikzcd}
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
So we need to find finite set \(l\) and a map \(e : n → l + 2\). We will construct those by
|
So we need to find a finite set \(l\) and a map \(e : n → l + 2\). We will construct those by
|
||||||
effectively constructing the coequilizer in \FinSet. So we take the quotient \(\faktor{n+2}{~}\)
|
effectively constructing the coequalizer in \FinSet. So we take the quotient \(\faktor{n+2}{\sim}\)
|
||||||
where \(~\) is the equivalence relation generated by the relation of having a joint preimage under
|
where \(\sim\) is the equivalence relation generated by the relation of having a joint preimage under
|
||||||
\(f\) and \(g\). We will now argue that our equalizer would be empty if this quotient identifies
|
\(f\) and \(g\). We will now argue that our equalizer would be empty if this quotient identifies
|
||||||
\(⊤\) and \(⊥\).
|
\(⊤\) and \(⊥\).
|
||||||
|
|
||||||
|
@ -543,19 +572,19 @@ And we arrive at the conclusion we wanted to get to:
|
||||||
Because \(⊥\) and \(⊤\) are being identified, there exists two finite sequence of elements \(x_i\) and \(y_i\) in \(m\), such that
|
Because \(⊥\) and \(⊤\) are being identified, there exists two finite sequence of elements \(x_i\) and \(y_i\) in \(m\), such that
|
||||||
there exists a \(k\) and
|
there exists a \(k\) and
|
||||||
(WLOG) \(f(x_1) = ⊥\), \(g(x_i) = f(y_i)\), \(g(y_i) = f(x_{i+1})\) and \(g(y_k) = ⊤\).
|
(WLOG) \(f(x_1) = ⊥\), \(g(x_i) = f(y_i)\), \(g(y_i) = f(x_{i+1})\) and \(g(y_k) = ⊤\).
|
||||||
Plugging that into the definition of \(j\) we get
|
Plugging that into the definition of \(j\), we get
|
||||||
\begin{align*}
|
\begin{align*}
|
||||||
⊥ = j(f)(h)(x_1) &= j(g)(h)(x_1) = j(f)(h)(y_1) \\ &= j(g)(h)(y_1) = j(f)(h)(x_2) = … = j(g)(h)(y_k) = ⊤
|
⊥ = j(f)(h)(x_1) &= j(g)(h)(x_1) = j(f)(h)(y_1) \\ &= j(g)(h)(y_1) = j(f)(h)(x_2) = … = j(g)(h)(y_k) = ⊤
|
||||||
\end{align*}
|
\end{align*}
|
||||||
which is a contradiction and thus \(⊤\) and \(⊥\) are not identified.
|
which is a contradiction and thus \(⊤\) and \(⊥\) are not identified.
|
||||||
For \(e : n → l + 2\) we take the evident quotient map restricted to \(n\).
|
For \(e : n → l + 2\), we take the evident quotient map restricted to \(n\).
|
||||||
While we now have our candidate, we still need to show that this is actually a pushout in \FL. As \FL is well pointed
|
While we now have our candidate, we still need to show that this is actually a pushout in \FL. As \FL is well pointed
|
||||||
it suffices to check global elements, which again are just elements in the set theoretic sense.
|
it suffices to check global elements, which again are just elements in the set theoretic sense.
|
||||||
As \(fe = ge\) by construction and \(j\) is a functor we get \(j(f)j(e) = j(g)j(e)\).
|
As \(fe = ge\) by construction and \(j\) is a functor we get \(j(f)j(e) = j(g)j(e)\).
|
||||||
|
|
||||||
Again let \(h ∈ 𝟚^n\) such that \(j(f)(h) = j(g)(h)\). We can then define
|
Again let \(h ∈ 𝟚^n\) such that \(j(f)(h) = j(g)(h)\). We can then define
|
||||||
\begin{align*}
|
\begin{align*}
|
||||||
h': l → 𝟚 & & h'(x) ≔ h(z) & & z ∈ e^{-1}(x)
|
h': l → 𝟚 && \text{by} && h'(x) ≔ h(z) & & \text{where} && z ∈ e^{-1}(x)\text{.}
|
||||||
\end{align*}
|
\end{align*}
|
||||||
For this definition to make sense we need to argue that the choice of \(z\) does not matter.
|
For this definition to make sense we need to argue that the choice of \(z\) does not matter.
|
||||||
So let \(z\) and \(z'\) be both element of \(e^{-1}(x)\). Like above that means there are
|
So let \(z\) and \(z'\) be both element of \(e^{-1}(x)\). Like above that means there are
|
||||||
|
@ -565,27 +594,22 @@ And we arrive at the conclusion we wanted to get to:
|
||||||
\begin{align*}
|
\begin{align*}
|
||||||
h(z) = j(f)(h)(x_1) &= j(g)(h)(x_1) = j(f)(h)(y_1) \\ &= j(g)(h)(y_1) = j(f)(h)(x_2) = … = j(g)(h)(y_k) = h(z')
|
h(z) = j(f)(h)(x_1) &= j(g)(h)(x_1) = j(f)(h)(y_1) \\ &= j(g)(h)(y_1) = j(f)(h)(x_2) = … = j(g)(h)(y_k) = h(z')
|
||||||
\end{align*}
|
\end{align*}
|
||||||
We also need that the map \(j(e)\) is monic, but this follows directly from the fact, that \(e\) in \FinSet is epic.
|
We also need that the map \(j(e)\) is monic, but this follows directly from the fact that \(e\) in \FinSet is epic.
|
||||||
|
|
||||||
We only need to produce a map \(B → 𝟚^l\), that commutes. We get this map directly, because we have shown that
|
We only need to produce a map \(B → 𝟚^l\), that commutes. We get this map directly, because we have shown that
|
||||||
this diagram is an equalizer in \FL.
|
this diagram is an equalizer in \FL.
|
||||||
|
This means we fulfill the conditions of \cref{lem:pullbackMono} and thus \(j_!\) preserves monomorphisms.
|
||||||
This means we fulfill the conditions of \fref{lem:pullbackMono} and thus \(j_!\) preserves monomorphisms.
|
|
||||||
\end{proof}
|
\end{proof}
|
||||||
|
|
||||||
\subsection{Step *}
|
\subsection{\(i^*j_!\) and \(j^*i_!\) induce an equivalence of homotopy categories}
|
||||||
By Ken Browns lemma we now that left Quillen functors preserve weak equivalences between cofibrant objects.
|
Before we continue our plan directly, we take a short detour to get a little bit better idea how these two functors behave.
|
||||||
In our setting every object is cofibrant, so all for functors preserve weak equivalences. Thus all for functors
|
|
||||||
descend to functors of the underlying homotpoy categories.
|
|
||||||
|
|
||||||
\subsection{Step 3}
|
From the previous sections it is immediately clear that \(i^*j_!\) and \(j^*i_!\) are left Quillen functors with some right adjoint.
|
||||||
|
One might ask if these two functors are adjoint to each other. The former development would suggest that they aren't
|
||||||
For \(i_!j^*\) and \(i^*j_!\) to be a potential quillen equivalence, they need to adjoint. So we continue by showing that.
|
and that is indeed the case.
|
||||||
To do that we first verify the claim that \(i^*j_!\) is indeed the triangulation functor.
|
|
||||||
|
|
||||||
\begin{definition}\label{def:triangulation}
|
\begin{definition}\label{def:triangulation}
|
||||||
Let \(t: □ → \Δ\) be the functor that sends \([1]^n \mapsto (Δ^1)^n\). The \emph{triangulation functor \(\T\)}
|
Let \(t: □ → \Δ\) be the functor that sends \([1]^n \mapsto (Δ^1)^n\). The \emph{triangulation functor \(\T\)}
|
||||||
is the left Kan extension of \(t\) along yoneda.
|
is the left Kan extension of \(t\) along Yoneda.
|
||||||
\begin{eqcd*}
|
\begin{eqcd*}
|
||||||
□ \arrow[r,"t"] \arrow[d,"\Yo"] & \Δ \\
|
□ \arrow[r,"t"] \arrow[d,"\Yo"] & \Δ \\
|
||||||
\□ \arrow[ru,"\T"] &
|
\□ \arrow[ru,"\T"] &
|
||||||
|
@ -596,76 +620,156 @@ To do that we first verify the claim that \(i^*j_!\) is indeed the triangulation
|
||||||
The functor \(i^*j_!\) is the triangulation functor.
|
The functor \(i^*j_!\) is the triangulation functor.
|
||||||
\end{proposition}
|
\end{proposition}
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
As \T is the unique cocontinues functor that extends product preserving functor from □ to \Δ that sends the interval
|
As \T is the unique cocontinuous functor that extends the product preserving functor from \□ to \Δ that sends the interval
|
||||||
to the interval, we only need to show these conditions. \(i^*j_!\) is cocontinues as it is the composition of two left
|
to the interval, we only need to show these conditions. \(i^*j_!\) is cocontinuous as it is the composition of two left
|
||||||
adjoints. We need to show that this functor is product preserving on representables. But by and
|
adjoints. We need to show that this functor is product preserving on representables. But by Yoneda and \cref{prop:j_!Nothing}
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
j_!(\I^n × \I^m) = j_!(\I^{n+m}) = \Yo 𝟚^{n+m} = \Yo 𝟚^n × \Yo 𝟚^m = j_!(\I^n) × j_!(\I^m)
|
j_!(\I^n × \I^m) = j_!(\I^{n+m}) = \Yo 𝟚^{n+m} = \Yo 𝟚^n × \Yo 𝟚^m = j_!(\I^n) × j_!(\I^m)
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
and \(i^*\) is a right adjoint we get this property immediatly. We also need to show that \(i^*j_!\) preserves the interval.
|
\(j_!\) preserves products of representables.
|
||||||
We already know this for \(j_!\). So the question ist if \(i^*\) preserves the interval. We now that \(i^*(\I)(x) =
|
Because \(i^*\) is a right adjoint we get this property immediately. We also need to show that \(i^*j_!\) preserves the interval.
|
||||||
|
We already know this for \(j_!\). So the question is if \(i^*\) preserves the interval. We now that \(i^*(\I)(x) =
|
||||||
\Hom_{\dCube}(\Yo [1],i(x))\). As \(i\) is fully faithful the claim follows.
|
\Hom_{\dCube}(\Yo [1],i(x))\). As \(i\) is fully faithful the claim follows.
|
||||||
\end{proof}
|
\end{proof}
|
||||||
|
|
||||||
The main insight from that this adjunction tells us, is that simplicials can't see connections. Or in other word degenerating
|
\begin{example}
|
||||||
a simplex along a connection is the same as degenrating it along a projection. While this is relatively easy to see from
|
|
||||||
an intuitive standpoint it is a bit tedious to actually show.
|
|
||||||
|
|
||||||
\begin{lemma}\label{lem:trianglesDon'tSeeConnections}
|
|
||||||
We have the following natural bijection
|
|
||||||
\begin{equation*}
|
\begin{equation*}
|
||||||
\Hom_{\□}(j^*i_!(Δ^n),\I^m) = \Hom_{\Δ}(Δ^n,i^*j_!(\I^m))
|
\Hom_{\□}(j^*i_!(Δ^2),\I^2) ≠ \Hom_{\Δ}(Δ^2,i^*j_!(\I^2))
|
||||||
\end{equation*}
|
\end{equation*}
|
||||||
\end{lemma}
|
\end{example}%
|
||||||
|
Intuitively the reason for this is that we can't map a square with one side degenerated to a triangle into the representable
|
||||||
|
square in \□. But we have a lot of ways to map a triangle into a triangulated square in \Δ.
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
Using that \(j_!\) and \(i_!\) preserve representables by \cref{prop:i_!Nothing,prop:j_!Nothing} , using the yoneda lemma on the right and expand the definition
|
By the Yoneda lemma and that \(j^*i_!\) is the triangulation functor, a map on the right-hand side corresponds to a
|
||||||
on the left we get the following.
|
pair of monotone maps \([2] → [1]\). There are 16 of such pairs. On the left we can use \cref{prop:j_!Nothing},
|
||||||
\begin{equation*}
|
and expanding the definition to get \(\Hom_{\□}(\Hom_{\FL}(j(-),[2]),\Hom_{□}(-,2))\). Lets take such a transformation
|
||||||
\Hom_{\□}(\Hom_{\FL}(j(-),[n]),\Hom_□(-,m)) = \Hom_{\FL}([n],𝟚^m)
|
and call it \(η\). \(η_0\) gives rise to a map \(f : [2] → 𝟚^2\). \(η_1\) witnesses that \(f\) is indeed monotone, by
|
||||||
\end{equation*}
|
composing with face maps. And \(η_2\) rules out all injective maps, as for them always exactly 2 faces agree and
|
||||||
So given a natural transformation \(η : \Hom_{\FL}(j(-),[n]) → \Hom_□(-,n)\), we define \(f: [n] → 𝟚^m\). For this we identify
|
\(\I^2(2)\) does not contain such faces. There are only 9 such maps, which is an upper bound for the possible number of
|
||||||
an element \(x\) of a finite lattice \(Y\) with the monotone map \(x : 𝟚^0 → Y\) sending the one point to \(x\). If we plug
|
natural transformations.
|
||||||
such an \(x\) into \(η_0\), we get a map \(η_0(x) : 0 → m\) in \□, or in other words a function \(m → 2\), which we
|
|
||||||
can identify with an element of \(𝟚^m\). Monotonicity is witnessed by \(η_1\). Translating \(f\) back to a function
|
|
||||||
\(η_0\) bijectively is trivial, we only need to show that \(η_0\) already determines all of \(η\). So assume we have
|
|
||||||
\(η_l\) already defined, we want to define \(η_{l+1}\). We only need to care about non degenerated cells, as these are
|
|
||||||
already forced by the lower data. For these non degenrate cases there is at most one candidate aligning with the face maps
|
|
||||||
to lower data. Using monotonicity of \(f\) we can see that these align correctly, and thus we ge a unique \(η\) given \(f\).
|
|
||||||
\end{proof}
|
\end{proof}
|
||||||
\todo{compute the last part, but that would be at least 3 lemmas and a 2 pages}
|
|
||||||
\todo{is it true at all? It has to be else everything else is wrong too. But can i map a triangle into a square?
|
\begin{example}
|
||||||
on the right side for sure}
|
\begin{equation*}
|
||||||
\begin{proposition}\label{prop:adjoints}
|
\Hom_{\Δ}(i^*j_!(\I^2),Δ^1 × Δ^1) ≠ \Hom_{\□}(\I^2,j^*i_!(Δ^1 × Δ^1))
|
||||||
\(j^*i_!\) is left adjoint to \(i^*j_!\)
|
\end{equation*}
|
||||||
\end{proposition}
|
\end{example}%
|
||||||
|
Here the problem is that the square made from a product in \Δ doesn't have a 2-cell that fills the whole square, this
|
||||||
|
doesn't give us a way to map the representable square on it without degenerating something. While if we triangulate the representable square
|
||||||
|
first we don't run into that problem.
|
||||||
\begin{proof}
|
\begin{proof}
|
||||||
As we already know that the left adjoint is cocontinuous, we only need to check this for representables in the
|
As \(j^*i_!\) is the triangulation functor, the left-hand side becomes \(\Hom_{\Δ}(Δ^1 × Δ^1,Δ^1 × Δ^1)\).
|
||||||
left component.
|
We can write \( Δ^1 × Δ^1 \) as a pushout of two copies of \(Δ^1\) joint by an edge.
|
||||||
\begin{equation*}
|
As \(i_!\) is cocontinuous, we can construct this pushout in \FL. By this and \cref{prop:i_!Nothing}, we
|
||||||
\Hom_{\□}(j^*i_!(Δ^n),B) = \Hom_{\Δ}(Δ^n,i^*j_!(B))
|
get a colimit of two representables there. Unraveling these definition it is a straightforward exercise
|
||||||
\end{equation*}
|
to verify that the set of on the left-hand side has more elements.
|
||||||
We can decomposition \(B\) into a cubical cell complex \cref{??}, a morphism from \(j^*i_!
|
|
||||||
\end{proof}
|
\end{proof}
|
||||||
\todo{somehow handle that we can get a cell decomposition of \(B\) (cite something?)}
|
|
||||||
|
|
||||||
From here on we follow the argument from \cite[§6.2]{solution}.
|
From here on we follow the argument from \cite[§6.2]{solution}. They lay down a criterion on functors and model categories
|
||||||
What we still need to show is that the unit and couint of the adjunction \(i_!j^* ⊣ i^*j_!\) are valued
|
such that every natural transformation between them is a weak equivalence. Thus we only need to construct any natural
|
||||||
in weak equivalences.
|
transformation between the identity functor and the concatenation of these functors.
|
||||||
|
|
||||||
For this we need a technical Lemma about Eilenberg-Zilber categories. But to make sense of its claim we first need
|
For this, we cite two technical
|
||||||
to introduce a technicality. If we have a category \A and presheafs on it. Then the automorphism group of some
|
lemmas whose theory is mostly developed in \cite{riehlTheoryPracticeReedy2014}, but are taken in this form from \cite{solution}.
|
||||||
|
To make sense of the first lemma we need
|
||||||
|
to introduce a technicality. If we have a category \A and presheaves on it, then the automorphism group of some
|
||||||
\(a ∈ \A\) acts on \(\Yo a\,b\) by composition. This kind of acting is natural in the sense that \(\Yo a f\) is an
|
\(a ∈ \A\) acts on \(\Yo a\,b\) by composition. This kind of acting is natural in the sense that \(\Yo a f\) is an
|
||||||
\(\mathrm{Aut}(a)\) equivariant map. Thus we can say \(\mathrm{Aut}(a)\) acts on \(\Yo a\). And thus we can also
|
\(\mathrm{Aut}(a)\)-equivariant map. Thus we can say \(\mathrm{Aut}(a)\) acts on \(\Yo a\). And thus we can also
|
||||||
quotient \(\Yo a\) by subgroups of \(\mathrm{Aut}(a)\).
|
quotient \(\Yo a\) by subgroups of \(\mathrm{Aut}(a)\). This is also where equivariance comes into play again, as
|
||||||
|
equivariance by definition guarantees us that these quotients of representables by some automorphism subgroup are
|
||||||
|
contractible.
|
||||||
|
|
||||||
|
\todo{if time and resources explain and proof these lemma (ca. 4 pages)}
|
||||||
\begin{lemma}[{\cites[§5]{riehlTheoryPracticeReedy2014}[lemma 6.2.13]{solution}}]\label{lem:Eilenberg-ZilberMonosCreated}
|
\begin{lemma}[{\cites[§5]{riehlTheoryPracticeReedy2014}[lemma 6.2.13]{solution}}]\label{lem:Eilenberg-ZilberMonosCreated}
|
||||||
Let \A be an Eilenberg-Zilber category. Then the monomorphism in \(\hat{\A}\) are generated under
|
Let \A be an Eilenberg-Zilber category. Then the monomorphisms in \(\hat{\A}\) are generated under
|
||||||
coproduct, pushout, sequential composition, and right cancelation under monomorphisms by the maps
|
coproduct, pushout, sequential composition, and right cancellation under monomorphisms by the maps
|
||||||
\(∅ → \faktor{\Yo a}{H}\) valued in the quotient of a representable presheaf at some \(a ∈ \A\) by an arbitrary
|
\(∅ → \faktor{\Yo a}{H}\) valued in the quotient of a representable presheaf at some \(a ∈ \A\) by an arbitrary
|
||||||
subgroup \(H\) of its automorphism group.
|
subgroup \(H\) of its automorphism group.
|
||||||
\end{lemma}
|
\end{lemma}
|
||||||
\todo{if there is time (lol) proof and explain the theory behind this}
|
|
||||||
|
|
||||||
|
\begin{lemma}[{\cites[§5]{riehlTheoryPracticeReedy2014}[lemma 6.2.15]{solution}}]\label{lem:PairClosure}
|
||||||
|
Let \(U,V : K → M\) be a cocontinuous pair of functors valued in a model category and \(α : U ⇒ V\) a
|
||||||
|
natural transformation between them. Define the cofibrations in \(K\) to be the maps that are sent to
|
||||||
|
cofibrations under both \(U\) and \(V\). Define \(\mathcal{N}\) to be the class of cofibrations
|
||||||
|
between cofibrant objects that are sent by Leibniz pushout application with \(α\) to weak equivalences in
|
||||||
|
\(M\). Then \(\mathcal{N}\) is closed under coproducts, pushout, (transfinite) composition, and right cancellation
|
||||||
|
between cofibrations.
|
||||||
|
\end{lemma}
|
||||||
|
|
||||||
|
\begin{corollary}[{\cite[corollary 6.2.16]{solution}}]\label{lem:everythingWorks}
|
||||||
|
Let \A be an Eilenberg–Zilber category and consider a parallel pair of functors \(U, V : \Set^{\A^\op} → M\) valued in a model
|
||||||
|
category \(M\) together with a natural transformation \(α : U ⇒ V\) . Suppose that \(U\) and \(V\) preserve colimits and send monomorphisms
|
||||||
|
in \(K\) to cofibrations in \(M\). Then if the components of \(α\) at quotients of representables by subgroups of their automorphism groups
|
||||||
|
are weak equivalences, then all components of \(α\) are weak equivalences.
|
||||||
|
\end{corollary}
|
||||||
|
\begin{proof}
|
||||||
|
By \cref{test}\todo{In Leibniz construction chapter make this an example} we can write the the part of \(α\) at \(X\) as a
|
||||||
|
Leibniz application with the monomorphism \(∅ → X\). We can use both lemmas from above to show that \(α\) gets send by all
|
||||||
|
of those maps to a weak equivalence. By \cref{lem:Eilenberg-ZilberMonosCreated} the monomorphisms in \(\Set^{\A^\op}\) are generated by
|
||||||
|
morphisms \(∅ → \faktor{\Yo a}{H}\) under some closure properties. By assumption, morphisms of that form are sent to weak equivalences
|
||||||
|
by the Leibniz application with \(α\). By \cref{lem:PairClosure}, the maps that get send to weak equivalences by Leibniz application with
|
||||||
|
\(α\) have the same closure properties, thus all monomorphisms get send to weak equivalences, and with them all morphisms of the
|
||||||
|
form \(∅ → X\).
|
||||||
|
\end{proof}
|
||||||
|
|
||||||
|
\begin{corollary}[{\cite[Corollary 6.2.17]{solution}}]\label{cor:dafuq}
|
||||||
|
Let \A be an Eilenberg–Zilber category for which \(\Set^{\A^\op}\) admits a model structure whose cofibrations are the monomorphisms,
|
||||||
|
in which the
|
||||||
|
quotients \(\faktor{\Yo a}{H}\) of representables by subgroups of their automorphism groups are weakly contractible. Then if
|
||||||
|
\(U, V : \Set^{\A^\op} → M\) define a
|
||||||
|
pair of left Quillen functors that preserve the terminal object, then any natural transformation \(α : U ⇒ V\) is a natural weak equivalence.
|
||||||
|
\end{corollary}
|
||||||
|
\begin{proof}
|
||||||
|
By Ken Browns lemma, left Quillen functors preserve weak equivalences between cofibrant objects. If such a functor preserves the terminal
|
||||||
|
object, then it also preserves weak contractibility between cofibrant objects. To apply \cref{lem:everythingWorks}
|
||||||
|
we need show that \(α_{\faktor{\Yo a}{H}}\) is a weak equivalence. As this is weakly contractible, we get the following commuting
|
||||||
|
square.
|
||||||
|
\begin{eqcd*}[column sep=large, row sep=large]
|
||||||
|
U\left(\faktor{\Yo a}{H}\right) \arrow[r,"α_{\faktor{\Yo a}{H}}"] \arrow[d, "\rotatebox{90}{\(\sim\)}"] & V\left(\faktor{\Yo a}{H}\right) \arrow[d, "\rotatebox{90}{\(\sim\)}"] \\
|
||||||
|
U(*) \arrow[r,equal] & V(*)
|
||||||
|
\end{eqcd*}
|
||||||
|
And by 2-out-of-3, the upper map must be a weak equivalence, and thus by \cref{lem:everythingWorks} the claim follows.
|
||||||
|
\end{proof}
|
||||||
|
|
||||||
|
\begin{theorem}
|
||||||
|
\(j^*i_!\) and \(i^*j_!\) induce an equivalence between \(\Ho(\□)\) and \(\Ho(\Δ)\).
|
||||||
|
\end{theorem}
|
||||||
|
\begin{proof}
|
||||||
|
By \cref{prop:i*preservesMonos,prop:i*preservesTrivialCofib,prop:i!preservesMonos,prop:i!preservesTrivialCofib,%
|
||||||
|
prop:j!preservesTrivialCofib,prop:j!preservesMonos,prop:j*preservesMonos,prop:j^*preservesTrivialCofib}, are
|
||||||
|
\(i^*\),\(i_!\),\(j^*\), and \(j_!\) left Quillen functors, and thus \(j^*i_!\) and \(i^*j_!\) too.
|
||||||
|
By Ken Browns lemma we know that left Quillen functors preserve weak equivalences between cofibrant objects. In
|
||||||
|
the model structures on \□ and \Δ, every monomorphism a cofibration and thus every object cofibrant.
|
||||||
|
Thus \(j^*i_!\) and \(i^*j_!\) preserve weak equivalences and descend to functors between the corresponding
|
||||||
|
homotopy categories.
|
||||||
|
|
||||||
|
To show that these induce an equivalence between the homotopy categories we must show that we have a zigzag of
|
||||||
|
natural transformations between \(i^*j_!j^*i_!\) and the identity functor such that every natural transformation
|
||||||
|
is valued in weak equivalences, and likewise for \(j^*i_!i^*j_!\). We will call \(η^i\) and \(ε^i\) the unit and counit
|
||||||
|
of the adjunction \(i_! ⊣ i^*\). Likewise \(η^j\) and \(ε^j\) for the adjunction \(j_! ⊣ j^*\).
|
||||||
|
We can construct these as follows
|
||||||
|
\begin{eqcd*}[column sep=large, row sep=large,execute at end picture={\draw[decorate,decoration={brace,mirror,amplitude=4.5}] (sBrcs.south) to (eBrcs.south);}]
|
||||||
|
\Δ \arrow[r,"i_!", ""'{name=i!s}] & |[alias=sBrcs]| \dcSet \arrow[r,"j^*"] \arrow[d,phantom,"⊛"] \arrow[rr,bend right=20,phantom , ""'{name=cc}] & \□ \arrow[r,"j_!"] & |[alias=eBrcs]| \dcSet \arrow[r,"i^*", ""'{name=i*s}] \arrow[d,phantom,"⊛"] & \Δ \\
|
||||||
|
\Δ \arrow[r,"i_!"{name=i!t}] & \dcSet \arrow[rr,"\id"{name=sida},""'{name=sidb}, equal] & & \dcSet \arrow[r,"i^*"{name=i*t}] & \Δ \\
|
||||||
|
\Δ \arrow[rrrr,"\id"{name=lid}, equal] & & & & \Δ
|
||||||
|
\arrow[Rightarrow ,from=i!s, to=i!t, "\id"]
|
||||||
|
\arrow[Rightarrow, from=cc, to=sida, "ε^j"]
|
||||||
|
\arrow[Rightarrow, from=i*s, to=i*t, "\id"]
|
||||||
|
\arrow[Rightarrow, from=lid, to=sidb, "η^i"]
|
||||||
|
\end{eqcd*}
|
||||||
|
and
|
||||||
|
\begin{eqcd*}[column sep=large, row sep=large,execute at end picture={\draw[decorate,decoration={brace,mirror,amplitude=4.5}] (sBrcs.south) to (eBrcs.south);}]
|
||||||
|
\□ \arrow[r,"j_!", ""'{name=j!s}] & |[alias=sBrcs]| \dcSet \arrow[r,"i^*"] \arrow[d,phantom,"⊛"] \arrow[rr,bend right=20,phantom, ""'{name=cc}] & \Δ \arrow[r,"i_!"] & |[alias=eBrcs]| \dcSet \arrow[r,"j^*", ""'{name=j*s}] \arrow[d,phantom,"⊛"] & \□ \\
|
||||||
|
\□ \arrow[r,"j_!"{name=j!t}] & \dcSet \arrow[rr,"\id"{name=sida},""'{name=sidb}, equal] & & \dcSet \arrow[r,"j^*"{name=j*t}] & \□ \\
|
||||||
|
\□ \arrow[rrrr,"\id"{name=lid}, equal] & & & & \□
|
||||||
|
\arrow[Rightarrow ,from=j!s, to=j!t, "\id"]
|
||||||
|
\arrow[Rightarrow, from=cc, to=sida, "ε^i"]
|
||||||
|
\arrow[Rightarrow, from=j*s, to=j*t, "\id"]
|
||||||
|
\arrow[Rightarrow, from=lid, to=sidb, "η^j"]
|
||||||
|
\end{eqcd*}
|
||||||
|
where \(⊛\) is the Godement product.
|
||||||
|
By \cref{prop:i_!Nothing,prop:j_!Nothing}, \(i_!\) and \(j_!\) preserve terminal obejcts and \(i^*\) and \(j^*\) do so because they are
|
||||||
|
right adjoints. So by \cref{cor:dafuq} these two cospans of natural transformations are weak equivalences and thus we have our
|
||||||
|
desired equivalence of homotopy categories.
|
||||||
|
\end{proof}
|
||||||
\end{document}
|
\end{document}
|
||||||
|
|
|
@ -1,5 +1,5 @@
|
||||||
\documentclass[../Main.tex]{subfiles}
|
\documentclass[../Main.tex]{subfiles}
|
||||||
\begin{document}
|
\begin{document}
|
||||||
\subfile{Model_Structure_Argument}
|
\subfile{Equivalence}
|
||||||
|
|
||||||
\end{document}
|
\end{document}
|
||||||
|
|
140
src/resource.bib
140
src/resource.bib
|
@ -33,6 +33,22 @@
|
||||||
file = {/home/nerf/Zotero/storage/XTZNK2WW/Angiuli et al. - 2018 - Cartesian Cubical Computational Type Theory Const.pdf}
|
file = {/home/nerf/Zotero/storage/XTZNK2WW/Angiuli et al. - 2018 - Cartesian Cubical Computational Type Theory Const.pdf}
|
||||||
}
|
}
|
||||||
|
|
||||||
|
@online{awodeyCartesianCubicalModel2023,
|
||||||
|
title = {Cartesian Cubical Model Categories},
|
||||||
|
author = {Awodey, Steve},
|
||||||
|
date = {2023-07-14},
|
||||||
|
eprint = {2305.00893},
|
||||||
|
eprinttype = {arXiv},
|
||||||
|
eprintclass = {math},
|
||||||
|
doi = {10.48550/arXiv.2305.00893},
|
||||||
|
url = {http://arxiv.org/abs/2305.00893},
|
||||||
|
urldate = {2024-08-03},
|
||||||
|
abstract = {The category of Cartesian cubical sets is introduced and endowed with a Quillen model structure using ideas coming from recent constructions of cubical systems of univalent type theory.},
|
||||||
|
pubstate = {prepublished},
|
||||||
|
keywords = {18N40 18B25 18N45,Mathematics - Algebraic Topology,Mathematics - Category Theory,Mathematics - Logic},
|
||||||
|
file = {/home/nerf/Zotero/storage/KWCXVX7B/Awodey - 2023 - Cartesian cubical model categories.pdf;/home/nerf/Zotero/storage/PNTHDEYX/2305.html}
|
||||||
|
}
|
||||||
|
|
||||||
@book{awodeyCategoryTheory2006,
|
@book{awodeyCategoryTheory2006,
|
||||||
title = {Category {{Theory}}},
|
title = {Category {{Theory}}},
|
||||||
author = {Awodey, Steve},
|
author = {Awodey, Steve},
|
||||||
|
@ -383,6 +399,27 @@
|
||||||
file = {/home/nerf/Zotero/storage/SVIAPJW5/Gambino and Sattler - 2017 - The Frobenius Condition, Right Properness, and Uni.pdf;/home/nerf/Zotero/storage/DTMPA7ZW/1510.html;/home/nerf/Zotero/storage/NLPL6A6T/1510.html}
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file = {/home/nerf/Zotero/storage/SVIAPJW5/Gambino and Sattler - 2017 - The Frobenius Condition, Right Properness, and Uni.pdf;/home/nerf/Zotero/storage/DTMPA7ZW/1510.html;/home/nerf/Zotero/storage/NLPL6A6T/1510.html}
|
||||||
}
|
}
|
||||||
|
|
||||||
|
@article{gambinoPolynomialFunctorsPolynomial2013,
|
||||||
|
title = {Polynomial Functors and Polynomial Monads},
|
||||||
|
author = {Gambino, Nicola and Kock, Joachim},
|
||||||
|
date = {2013-01},
|
||||||
|
journaltitle = {Mathematical Proceedings of the Cambridge Philosophical Society},
|
||||||
|
shortjournal = {Math. Proc. Camb. Phil. Soc.},
|
||||||
|
volume = {154},
|
||||||
|
number = {1},
|
||||||
|
eprint = {0906.4931},
|
||||||
|
eprinttype = {arXiv},
|
||||||
|
eprintclass = {math},
|
||||||
|
pages = {153--192},
|
||||||
|
issn = {0305-0041, 1469-8064},
|
||||||
|
doi = {10.1017/S0305004112000394},
|
||||||
|
url = {http://arxiv.org/abs/0906.4931},
|
||||||
|
urldate = {2024-08-04},
|
||||||
|
abstract = {We study polynomial functors over locally cartesian closed categories. After setting up the basic theory, we show how polynomial functors assemble into a double category, in fact a framed bicategory. We show that the free monad on a polynomial endofunctor is polynomial. The relationship with operads and other related notions is explored.},
|
||||||
|
keywords = {18C15 18D05 18D50 03G30,Mathematics - Category Theory},
|
||||||
|
file = {/home/nerf/Zotero/storage/JMIDZIWR/Gambino and Kock - 2013 - Polynomial functors and polynomial monads.pdf;/home/nerf/Zotero/storage/CADCALSE/0906.html}
|
||||||
|
}
|
||||||
|
|
||||||
@article{garnerUnderstandingSmallObject2009,
|
@article{garnerUnderstandingSmallObject2009,
|
||||||
title = {Understanding the Small Object Argument},
|
title = {Understanding the Small Object Argument},
|
||||||
author = {Garner, Richard},
|
author = {Garner, Richard},
|
||||||
|
@ -453,6 +490,15 @@
|
||||||
file = {/home/nerf/Zotero/storage/VKM9TK2D/Hofmann - Doctor of Philosophy University of Edinburgh 1995.pdf}
|
file = {/home/nerf/Zotero/storage/VKM9TK2D/Hofmann - Doctor of Philosophy University of Edinburgh 1995.pdf}
|
||||||
}
|
}
|
||||||
|
|
||||||
|
@article{hofmannLiftingGrothendieckUniverses1997,
|
||||||
|
title = {Lifting {{Grothendieck Universes}}},
|
||||||
|
author = {Hofmann, Martin and Streicher, Thomas},
|
||||||
|
date = {1997-21},
|
||||||
|
url = {https://www2.mathematik.tu-darmstadt.de/~streicher/NOTES/lift.pdf},
|
||||||
|
langid = {english},
|
||||||
|
file = {/home/nerf/Zotero/storage/LE9B8IMD/Hofmann et al. - Lifting Grothendieck Universes.pdf}
|
||||||
|
}
|
||||||
|
|
||||||
@article{hofmannSyntaxSemanticsDependent,
|
@article{hofmannSyntaxSemanticsDependent,
|
||||||
title = {Syntax and {{Semantics}} of {{Dependent Types}}},
|
title = {Syntax and {{Semantics}} of {{Dependent Types}}},
|
||||||
author = {Hofmann, Martin},
|
author = {Hofmann, Martin},
|
||||||
|
@ -478,6 +524,23 @@
|
||||||
organization = {American Mathematical Society}
|
organization = {American Mathematical Society}
|
||||||
}
|
}
|
||||||
|
|
||||||
|
@online{hoveyModelCategories2007a,
|
||||||
|
title = {Model {{Categories}}},
|
||||||
|
author = {Hovey, Mark},
|
||||||
|
date = {2007-10-17},
|
||||||
|
series = {Mathematical {{Surveys}} and {{Monographs}}},
|
||||||
|
volume = {63},
|
||||||
|
publisher = {American Mathematical Society},
|
||||||
|
issn = {0076-5376, 2331-7159},
|
||||||
|
doi = {10.1090/surv/063},
|
||||||
|
url = {https://www.ams.org/surv/063},
|
||||||
|
urldate = {2024-08-02},
|
||||||
|
abstract = {Advancing research. Creating connections.},
|
||||||
|
isbn = {9780821843611 9781470412906},
|
||||||
|
langid = {english},
|
||||||
|
organization = {American Mathematical Society}
|
||||||
|
}
|
||||||
|
|
||||||
@online{IntroductionHomotopyTheory,
|
@online{IntroductionHomotopyTheory,
|
||||||
title = {Introduction to {{Homotopy Theory}} in {{nLab}}},
|
title = {Introduction to {{Homotopy Theory}} in {{nLab}}},
|
||||||
url = {https://ncatlab.org/nlab/show/Introduction+to+Homotopy+Theory},
|
url = {https://ncatlab.org/nlab/show/Introduction+to+Homotopy+Theory},
|
||||||
|
@ -625,6 +688,58 @@
|
||||||
file = {/home/nerf/Zotero/storage/IPQSVWQ9/Orton and Pitts - 2018 - Axioms for Modelling Cubical Type Theory in a Topo.pdf;/home/nerf/Zotero/storage/KRK2SGUB/1712.html}
|
file = {/home/nerf/Zotero/storage/IPQSVWQ9/Orton and Pitts - 2018 - Axioms for Modelling Cubical Type Theory in a Topo.pdf;/home/nerf/Zotero/storage/KRK2SGUB/1712.html}
|
||||||
}
|
}
|
||||||
|
|
||||||
|
@article{pareAbsoluteColimits1971,
|
||||||
|
title = {On Absolute Colimits},
|
||||||
|
author = {Paré, Robert},
|
||||||
|
date = {1971-09-01},
|
||||||
|
journaltitle = {Journal of Algebra},
|
||||||
|
shortjournal = {Journal of Algebra},
|
||||||
|
volume = {19},
|
||||||
|
number = {1},
|
||||||
|
pages = {80--95},
|
||||||
|
issn = {0021-8693},
|
||||||
|
doi = {10.1016/0021-8693(71)90116-5},
|
||||||
|
url = {https://www.sciencedirect.com/science/article/pii/0021869371901165},
|
||||||
|
urldate = {2024-07-10},
|
||||||
|
file = {/home/nerf/Zotero/storage/E68DYK76/0021869371901165.html}
|
||||||
|
}
|
||||||
|
|
||||||
|
@incollection{quillenAxiomaticHomotopyTheory1967,
|
||||||
|
title = {Axiomatic Homotopy Theory},
|
||||||
|
booktitle = {Homotopical {{Algebra}}},
|
||||||
|
author = {Quillen, Daniel G.},
|
||||||
|
editor = {Quillen, Daniel G.},
|
||||||
|
date = {1967},
|
||||||
|
pages = {1--64},
|
||||||
|
publisher = {Springer},
|
||||||
|
location = {Berlin, Heidelberg},
|
||||||
|
doi = {10.1007/BFb0097439},
|
||||||
|
url = {https://doi.org/10.1007/BFb0097439},
|
||||||
|
urldate = {2024-08-02},
|
||||||
|
isbn = {978-3-540-35523-6},
|
||||||
|
langid = {english},
|
||||||
|
keywords = {Double Coset,Homotopy Category,Homotopy Theory,Model Category,Weak Equivalence},
|
||||||
|
file = {/home/nerf/Zotero/storage/WIV7ECSM/Quillen - 1967 - Axiomatic homotopy theory.pdf}
|
||||||
|
}
|
||||||
|
|
||||||
|
@incollection{quillenExamplesSimplicialHomotopy1967,
|
||||||
|
title = {Examples of Simplicial Homotopy Theories},
|
||||||
|
booktitle = {Homotopical {{Algebra}}},
|
||||||
|
author = {Quillen, Daniel G.},
|
||||||
|
editor = {Quillen, Daniel G.},
|
||||||
|
date = {1967},
|
||||||
|
pages = {65--155},
|
||||||
|
publisher = {Springer},
|
||||||
|
location = {Berlin, Heidelberg},
|
||||||
|
doi = {10.1007/BFb0097440},
|
||||||
|
url = {https://doi.org/10.1007/BFb0097440},
|
||||||
|
urldate = {2024-08-02},
|
||||||
|
isbn = {978-3-540-35523-6},
|
||||||
|
langid = {english},
|
||||||
|
keywords = {Abelian Group,Exact Sequence,Projective Resolution,Simplicial Group,Spectral Sequence},
|
||||||
|
file = {/home/nerf/Zotero/storage/SV4WJESD/Quillen - 1967 - Examples of simplicial homotopy theories.pdf}
|
||||||
|
}
|
||||||
|
|
||||||
@book{quillenHomotopicalAlgebra1967,
|
@book{quillenHomotopicalAlgebra1967,
|
||||||
title = {Homotopical {{Algebra}}},
|
title = {Homotopical {{Algebra}}},
|
||||||
author = {Quillen, Daniel G.},
|
author = {Quillen, Daniel G.},
|
||||||
|
@ -643,6 +758,24 @@
|
||||||
file = {/home/nerf/Zotero/storage/JG33WVEZ/Quillen - 1967 - Homotopical Algebra.pdf}
|
file = {/home/nerf/Zotero/storage/JG33WVEZ/Quillen - 1967 - Homotopical Algebra.pdf}
|
||||||
}
|
}
|
||||||
|
|
||||||
|
@book{quillenHomotopicalAlgebra1967a,
|
||||||
|
title = {Homotopical {{Algebra}}},
|
||||||
|
author = {Quillen, Daniel G.},
|
||||||
|
editor = {Dold, A. and Eckmann, B.},
|
||||||
|
editortype = {redactor},
|
||||||
|
date = {1967},
|
||||||
|
series = {Lecture {{Notes}} in {{Mathematics}}},
|
||||||
|
volume = {43},
|
||||||
|
publisher = {Springer},
|
||||||
|
location = {Berlin, Heidelberg},
|
||||||
|
doi = {10.1007/BFb0097438},
|
||||||
|
url = {http://link.springer.com/10.1007/BFb0097438},
|
||||||
|
urldate = {2024-08-02},
|
||||||
|
isbn = {978-3-540-03914-3 978-3-540-35523-6},
|
||||||
|
keywords = {algebra,homotopical algebra,Homotopie,homotopy,homotopy theory,Quillen},
|
||||||
|
file = {/home/nerf/Zotero/storage/6JP38TF2/Quillen - 1967 - Homotopical Algebra.pdf}
|
||||||
|
}
|
||||||
|
|
||||||
@unpublished{riehlAlgebraicModelStructures2011,
|
@unpublished{riehlAlgebraicModelStructures2011,
|
||||||
title = {Algebraic Model Structures},
|
title = {Algebraic Model Structures},
|
||||||
author = {Riehl, Emily},
|
author = {Riehl, Emily},
|
||||||
|
@ -818,6 +951,13 @@
|
||||||
file = {/home/nerf/Zotero/storage/SYH7C9JV/Sattler - 2019 - Idempotent completion of cubes in posets.pdf;/home/nerf/Zotero/storage/9ZN8RBCZ/1805.html}
|
file = {/home/nerf/Zotero/storage/SYH7C9JV/Sattler - 2019 - Idempotent completion of cubes in posets.pdf;/home/nerf/Zotero/storage/9ZN8RBCZ/1805.html}
|
||||||
}
|
}
|
||||||
|
|
||||||
|
@online{Section00VCFunctoriality,
|
||||||
|
title = {Section 7.5 ({{00VC}}): {{Functoriality}} of Categories of Presheaves—{{The Stacks}} Project},
|
||||||
|
url = {https://stacks.math.columbia.edu/tag/00VC},
|
||||||
|
urldate = {2024-07-12},
|
||||||
|
file = {/home/nerf/Zotero/storage/LEP4E2FJ/00VC.html}
|
||||||
|
}
|
||||||
|
|
||||||
@online{shulmanAllInftyToposes2019,
|
@online{shulmanAllInftyToposes2019,
|
||||||
title = {All \$(\textbackslash infty,1)\$-Toposes Have Strict Univalent Universes},
|
title = {All \$(\textbackslash infty,1)\$-Toposes Have Strict Univalent Universes},
|
||||||
author = {Shulman, Michael},
|
author = {Shulman, Michael},
|
||||||
|
|
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Reference in a new issue