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\newtheorem{prop}{Proposition} \newtheorem{cor}{Corollary} \newtheorem*{utheorem}{Theorem} \newtheorem*{ulemma}{Lemma} \newtheorem*{uprop}{Proposition} \newtheorem*{ucor}{Corollary} \theoremstyle{definition} \newtheorem{defn}{Definition} \newtheorem{example}{Example} \newtheorem*{udefn}{Definition} \newtheorem*{uexample}{Example} \theoremstyle{remark} \newtheorem{remark}{Remark} \newtheorem{note}{Note} \newtheorem*{uremark}{Remark} \newtheorem*{unote}{Note} %------------------------------------------------------------------- \begin{document} %------------------------------------------------------------------- \section*{model structure on topological spaces} \hypertarget{context}{}\subsubsection*{{Context}}\label{context} \hypertarget{model_category_theory}{}\paragraph*{{Model category theory}}\label{model_category_theory} [[!include model category theory - contents]] \hypertarget{topology}{}\paragraph*{{Topology}}\label{topology} [[!include topology - contents]] \hypertarget{homotopy_theory}{}\paragraph*{{Homotopy theory}}\label{homotopy_theory} [[!include homotopy - contents]] \hypertarget{contents}{}\section*{{Contents}}\label{contents} \noindent\hyperlink{idea}{Idea}\dotfill \pageref*{idea} \linebreak \noindent\hyperlink{definition}{Definition}\dotfill \pageref*{definition} \linebreak \noindent\hyperlink{QuillenModelStructure}{Classical Quillen Model Structure}\dotfill \pageref*{QuillenModelStructure} \linebreak \noindent\hyperlink{StromModelStructure}{Hurewicz (or Str\o{}m) Model Structure}\dotfill \pageref*{StromModelStructure} \linebreak \noindent\hyperlink{mixed_model_structure}{Mixed Model Structure}\dotfill \pageref*{mixed_model_structure} \linebreak \noindent\hyperlink{properties}{Properties}\dotfill \pageref*{properties} \linebreak \noindent\hyperlink{OnNiceTopologicalSpaces}{Restriction to convenient categories of topological spaces}\dotfill \pageref*{OnNiceTopologicalSpaces} \linebreak \noindent\hyperlink{relation_between__and_}{Relation between $Top_{Quillen}$ and $sSet_{Quillen}$}\dotfill \pageref*{relation_between__and_} \linebreak \noindent\hyperlink{relation_between__and__2}{Relation between $Top_{Quillen}$ and $Top_{Strom}$}\dotfill \pageref*{relation_between__and__2} \linebreak \noindent\hyperlink{related_concepts}{Related concepts}\dotfill \pageref*{related_concepts} \linebreak \noindent\hyperlink{references}{References}\dotfill \pageref*{references} \linebreak \hypertarget{idea}{}\subsection*{{Idea}}\label{idea} Philosophically, [[model category|model structures]] allow one to [[localization|localize]] a [[category]] at a particular collection of [[category with weak equivalences|weak equivalences]], which one would like to formally invert. For [[topological space]]s, there are two natural candidates for the collection $W$ of weak equivalences: \begin{enumerate}% \item the [[weak homotopy equivalence]]s \item and the [[homotopy equivalence]]s. \end{enumerate} Both of these have accompanying model structures. Interestingly, these two model structures can also be combined to form what's known as the \emph{mixed} model structure. All of these model structures exist not only on the category of all topological spaces, but also on most [[convenient categories of topological spaces]]. Using a nice category instead is sometimes important, such as if we want the model structure to be [[monoidal model category|monoidal]]. \hypertarget{definition}{}\subsection*{{Definition}}\label{definition} \hypertarget{QuillenModelStructure}{}\subsubsection*{{Classical Quillen Model Structure}}\label{QuillenModelStructure} The first, and most prevalent, [[model category]] structure on [[Top]], called the \emph{[[classical model structure on topological spaces]]} (\hyperlink{Quillen67}{Quillen67, II.3}) has \begin{itemize}% \item weak equivalences are the [[weak homotopy equivalences]]; \item fibrations are the [[Serre fibrations]], maps which have the [[right lifting property]] with respect to all inclusions of the form $i_0 : D^n \hookrightarrow D^n \times I$ that include the $n$-disk as $D^n \times \{0\}$. \item cofibrations are the ``[[retracts]] of [[relative cell complexes]]''. \end{itemize} This is a [[cofibrantly generated model category]]. The cofibrations $C$ are generated by the set of [[boundary]] inclusions $S^{n-1} \hookrightarrow D^n$ for all $n \in \mathbb{N}$ in the sense that they are the smallest saturated class containing these morphisms. As a consequence, of Quillen's [[small object argument]], all cofibrations have the form described above, where a [[relative cell complex]] is a [[transfinite composition|transfinite composite]] of [[pushouts]] of [[coproducts]] of these generating maps. This model structure is sometimes called the \textbf{[[Quillen model structure on topological spaces]]} or \textbf{$q$-model structure} on [[Top]]. \hypertarget{StromModelStructure}{}\subsubsection*{{Hurewicz (or Str\o{}m) Model Structure}}\label{StromModelStructure} A second model structure has \begin{itemize}% \item weak equivalences are the [[homotopy equivalences]]; \item fibrations are the \textbf{[[Hurewicz fibration]]s}, which are defined to be maps that have the right lifting property with respect to \emph{all} inclusions $i_0 : A \hookrightarrow A \times I$ for any topological space $A$. \item cofibrations are determined by these classes and are called the \textbf{closed [[Hurewicz cofibration]]s}. \end{itemize} This model structure is sometimes called the \textbf{Hurewicz model structure}, since it uses Hurewicz fibrations and cofibrations, or also the $h$-model structure, where $h$ can stand for either ``Hurewicz'' or ``homotopy equivalence.'' However, it is also sometimes called the [[Strøm model structure]], since it was first proven to exist by [[Arne Strøm]]. \hypertarget{mixed_model_structure}{}\subsubsection*{{Mixed Model Structure}}\label{mixed_model_structure} From the definitions, [[Hurewicz fibration]]s are necessarily [[Serre fibration]]s. It is well-known that [[homotopy equivalence]]s are [[weak homotopy equivalence]]s. If we write $(C_1, F_1, W_1)$ for the classes of the first model structure and $(C_2, F_2, W_2)$ for the classes of the second, we have $W_2 \subset W_1$ and $F_2 \subset F_1$. In general given two model structures with these inclusions, we get a third \textbf{[[mixed model structure]]} $(C_m, F_2, W_1)$ where the cofibrations $C_m$ are determined by the other two classes. On topological spaces, this model structure has \begin{itemize}% \item weak equivalences the [[weak homotopy equivalence]]s \item fibrations the [[Hurewicz fibration]]s; \item cofibrant spaces (the [[m-cofibrant space]]s) are precisely those spaces that are homotopy equivalent to [[CW complex]]es. \end{itemize} \hypertarget{properties}{}\subsection*{{Properties}}\label{properties} \hypertarget{OnNiceTopologicalSpaces}{}\subsubsection*{{Restriction to convenient categories of topological spaces}}\label{OnNiceTopologicalSpaces} For the discussion of the [[homotopy theory]] given by the model structure on topological spaces, it is necessary or at least useful to pass to [[convenient categories of topological spaces]]. \begin{defn} \label{}\hypertarget{}{} Write \begin{itemize}% \item $kTop \hookrightarrow Top$ for the [[full subcategory]] of [[k-spaces]]; \item $CGTop \hookrightarrow Top$ for the full subcategory of [[compactly generated spaces]]. \end{itemize} \end{defn} \begin{prop} \label{}\hypertarget{}{} There is a [[model category]] structure $kTop_{Quillen}$ on $kTop$ in which a morphism is a cofibration, fibration or weak equivalence, respectively, precisely if it is so under the inclusion $kTop \hookrightarrow Top$. And this inclusion is the [[left adjoint]] in a [[Quillen equivalence]] \begin{displaymath} Top_{Quillen} \stackrel{\overset{}{\hookleftarrow}}{\underset{}{\to}} kTop_{Quillen} \,. \end{displaymath} \end{prop} This appears for instance as (\hyperlink{Hovey}{Hovey, theorem 2.4.23}) \begin{prop} \label{}\hypertarget{}{} There is a [[model category]] structure $CGTop_{Quillen}$ on $CGTop$ in which a morphism is a cofibration, fibration or weak equivalence, respectively, precisely if it is so under the inclusion $CGTop \hookrightarrow Top$. And this inclusion is the [[right adjoint]] in a [[Quillen equivalence]] \begin{displaymath} CGTop_{Quillen} \stackrel{\overset{w}{\leftarrow}}{\underset{}{\hookrightarrow}} kTop_{Quillen} \,. \end{displaymath} \end{prop} Notice that $Top_{Quillen}$ is \emph{not} a [[monoidal model category]], because $Top$ itself is not ([[cartesian closed category|cartesian]]) [[closed monoidal category|closed]]. \begin{prop} \label{}\hypertarget{}{} Both $kTop_{Quillen}$ and $CGTop_{Quillen}$ are [[symmetric monoidal category|symmetric]] [[monoidal model categories]]. \end{prop} This appears as (\hyperlink{Hovey}{Hovey, prop. 4.2.11}). \begin{prop} \label{}\hypertarget{}{} In fact $CGTop_{Quillen}$ is a [[cartesian closed model category]]. (see e.g \hyperlink{BergerMoerdijk03}{Berger-Moerdijk 03}) \end{prop} \hypertarget{relation_between__and_}{}\subsubsection*{{Relation between $Top_{Quillen}$ and $sSet_{Quillen}$}}\label{relation_between__and_} The \hyperlink{QuillenModelStructure}{Quillen model structure} $Top_{Qullen}$ is [[Quillen equivalence|Quillen equivalent]] to the standard (Quillen) [[model structure on simplicial sets]] via the total [[fundamental infinity-groupoid|singular complex]] and [[geometric realization]] functors. \begin{displaymath} (\vert-\vert \dashv Sing) : Top_{Quillen} \stackrel{\overset{|-|}{\leftarrow}}{\underset{Sing}{\to}} sSet_{Quillen} \,. \end{displaymath} Since the standard [[model structure on simplicial sets]] is a [[presentable (infinity,1)-category|presentation]] of the [[(∞,1)-category]] [[∞Grpd]] of [[∞-groupoid]]s realized as [[Kan complex]]es, this identifies topological spaces with [[∞-groupoid]]s in an [[(∞,1)-category|(∞,1)-categorical]] sense. Notably it says that every $\infty$-groupoid is, up to equivalence, the [[fundamental ∞-groupoid]] of some topological space. This statement is called the [[homotopy hypothesis]] (which here is a theorem). See there for more details. \hypertarget{relation_between__and__2}{}\subsubsection*{{Relation between $Top_{Quillen}$ and $Top_{Strom}$}}\label{relation_between__and__2} The identity functor constitutes a [[Quillen adjunction]] \begin{displaymath} (Id \dashv Id) : Top_{Strom} \stackrel{\leftarrow}{\to} Top_{Quillen} \end{displaymath} between the \hyperlink{QuillenModelStructure}{Quillen model structure} and the \hyperlink{StromModelStructure}{Strom model structure} on $Top$. Here $Top_{Strom} \to Top_{Quillen}$ is the [[Quillen adjunction|right Quillen functor]]. \hypertarget{related_concepts}{}\subsection*{{Related concepts}}\label{related_concepts} \begin{itemize}% \item [[homotopical structure on C\emph{-algebras]]} \end{itemize} \hypertarget{references}{}\subsection*{{References}}\label{references} The original ``Quillen'' or ``q-'' model structure is due to \begin{itemize}% \item [[Dan Quillen]], chapter II, section 3 of \emph{Homotopical algebra}, Lecture Notes in Mathematics \textbf{43}, Springer-Verlag 1967, iv+156 pp. \end{itemize} An expository, concise and comprehensive writeup is in \begin{itemize}% \item [[Philip Hirschhorn]], \emph{The Quillen model category of topological spaces}, 2015 (\href{http://arxiv.org/abs/1508.01942}{arXiv:1508.01942}) \end{itemize} Standard textbooks references include \begin{itemize}% \item [[Mark Hovey]] \emph{Model categories} \item Hirschhorn \emph{Model categories and their localizations}. \item [[Kate Ponto]], [[Peter May]], section 17 of \emph{More concise algebraic topology} (\href{http://www.maths.ed.ac.uk/~aar/papers/mayponto.pdf}{pdf}) \end{itemize} For the ``Hurewicz,'' ``Str\o{}m,'' or ``h-'' model structure: \begin{itemize}% \item [[Arne Strøm]], \emph{The homotopy category is a homotopy category}, Archiv der Mathematik 23 (1972) \end{itemize} For the ``mixed'' or ``m-'' model structure: \begin{itemize}% \item Michael Cole, \emph{Mixing model structures}, Topology Appl. 153 no. 7 (2006) \href{http://dx.doi.org/10.1016/j.topol.2005.02.004}{doi}. \end{itemize} The generalization to the [[model structure on topological operads]] is due to \begin{itemize}% \item [[Clemens Berger]], [[Ieke Moerdijk]], \emph{Axiomatic homotopy theory for operads}, Comment. Math. Helv. Vol. 78 (2003), no. 4 (\href{http://arxiv.org/abs/math/0206094}{arXiv:math/0206094}) \end{itemize} [[!redirects model category of topological spaces]] [[!redirects model structures on topological spaces]] [[!redirects model structures on Top]] \end{document}