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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*{proper morphism} \begin{quote}% For the concept in [[topology]] see at \emph{[[proper map]]}. \end{quote} \hypertarget{context}{}\subsubsection*{{Context}}\label{context} \hypertarget{geometry}{}\paragraph*{{Geometry}}\label{geometry} [[!include higher geometry - contents]] \hypertarget{contents}{}\section*{{Contents}}\label{contents} \noindent\hyperlink{definitions}{Definitions}\dotfill \pageref*{definitions} \linebreak \noindent\hyperlink{between_topological_spaces}{Between topological spaces}\dotfill \pageref*{between_topological_spaces} \linebreak \noindent\hyperlink{between_schemes}{Between schemes}\dotfill \pageref*{between_schemes} \linebreak \noindent\hyperlink{between_locales}{Between locales}\dotfill \pageref*{between_locales} \linebreak \noindent\hyperlink{between_toposes}{Between toposes}\dotfill \pageref*{between_toposes} \linebreak \noindent\hyperlink{related_concepts}{Related concepts}\dotfill \pageref*{related_concepts} \linebreak \noindent\hyperlink{references}{References}\dotfill \pageref*{references} \linebreak \hypertarget{definitions}{}\subsection*{{Definitions}}\label{definitions} \hypertarget{between_topological_spaces}{}\subsubsection*{{Between topological spaces}}\label{between_topological_spaces} While every [[continuous map]] sends [[compact subsets]] to [[compact subsets]] (see at \emph{[[continuous images of compact spaces are compact]]}), it is not true in general that the [[preimage]] of a compact set along a continuous map is compact. A [[continuous function]] $f : X \to Y$ between [[topological space]]s is \textbf{[[proper map]]} if the [[inverse image]] of any [[compact space|compact]] subset is itself compact. A notion of proper homotopy between proper maps leads to [[proper homotopy theory]]. Similarly, one can consider the conditions on morphisms in other geometric situations, like [[algebraic geometry]], and properness often either reflects or implies good behaviour with respect to the compact objects (cf. also proper push-forward). \hypertarget{between_schemes}{}\subsubsection*{{Between schemes}}\label{between_schemes} A \textbf{proper morphism of [[schemes]]} is by definition a morphism $f:X\to Y$ which is \begin{enumerate}% \item [[separated morphism|separated]], \item of [[finite type morphism|finite type]] \item [[universally closed morphism|universally closed]] (the latter means that for every $h: Z\to Y$ the pullback $h^*(f): Z\times_Y X\to Z$ is closed). \end{enumerate} There is a classical and very practical [[valuative criterion of properness]] due Chevalley. We say that a scheme $X$ is \textbf{proper} if the canonical map $X \to \operatorname{Spec} \mathbb{Z}$ to the [[terminal object]] is proper. Proper schemes are analogous to [[compact topological spaces]]. This is one reason why one uses the terminology ``quasi-compact'' when referring to schemes whose underlying topological space is compact. The [[base change]] formulas for [[cohomology]] for proper and for smooth morphisms of schemes motivated [[Alexander Grothendieck|Grothendieck]] (in [[Pursuing Stacks]]) to define abstract proper and smooth functors in the setting of [[fibered categories]]; this is further expanded on in (\hyperlink{Maltsiniotis}{Maltsiniotis}). \hypertarget{between_locales}{}\subsubsection*{{Between locales}}\label{between_locales} Recall that a [[locale]] $L$ is given by a [[frame]] $O(L)$, its [[frame of opens]], and that a [[continuous map]] $f$ from $K$ to $L$ is given by an [[adjunction]] $f^* \dashv f_* \colon O(K) \rightleftarrows O(L)$ such that the [[inverse image]] function $f^*$ preserves finitary [[meets]] (or equivalently is a frame [[homomorphism]], since it must preserve all [[joins]]). Such a map $f$ is \textbf{proper} iff the [[direct image]] function $f_*$ preserves [[directed joins]] (or equivalently is [[Scott-continuous function|Scott-continuous]], or equivalently is a morphism of [[preframes]]), and also satisfies the [[Frobenius reciprocity]]-like condition that $f_*(U\cup f^*(V)) = f_*(U) \cup V$ (which by itself states that the map is [[closed map|closed]]). In particular, the map $L\to 1$ is proper iff $L$ is both [[compact locale|compact]] and [[covert space|covert]]. But in this case the second condition is redundant, since every compact locale is automatically covert; see [[covert space]] for a proof. Proper maps of locales can also be characterized as those that are universally closed, i.e. every pullback of them (along any map of locales) is closed. \hypertarget{between_toposes}{}\subsubsection*{{Between toposes}}\label{between_toposes} Proper maps of locales can be generalized to [[geometric morphisms]] of [[Grothendieck toposes]]; see [[proper geometric morphism]]. The topos-theoretic condition refers only to directed unions of subterminal objects, suggesting a stronger condition that it preserve all [[filtered colimits]]. This is a strictly stronger condition even for locales (i.e. [[localic toposes]]), called being \emph{tidy}. In fact properness and tidiness are the first two rungs on an infinite ladder of higher properness for [[higher toposes]]. \hypertarget{related_concepts}{}\subsection*{{Related concepts}}\label{related_concepts} \begin{itemize}% \item [[proper map]], [[open map]], [[closed map]] \item [[open morphism]], [[closed morphism]] \item [[proper base change theorem]] \item [[proper homotopy theory]] \item [[maps from compact spaces to Hausdorff spaces are closed and proper]] \end{itemize} \hypertarget{references}{}\subsection*{{References}}\label{references} \begin{itemize}% \item [[Georges Maltsiniotis]], \emph{Structures d'asph\'e{}ricit\'e{}, foncteurs lisses, et fibrations}, Ann. Math. Blaise Pascal \textbf{12}, pp. 1-39 (2005) (\href{http://people.math.jussieu.fr/~maltsin/ps/asphbl.ps}{ps}). \end{itemize} (TO ADD: The definition of a proper dg algebra, proper dg category, proper A-inf cat ???) \begin{itemize}% \item wikipedia \href{http://en.wikipedia.org/wiki/Proper_morphism}{proper morphism} \item Daniel Halpern-Leistner, Anatoly Preygel, \emph{Mapping stacks and categorical notions of properness}, \href{http://arxiv.org/abs/1402.3204}{arxiv/1402.3204} \end{itemize} [[!redirects proper morphism]] [[!redirects proper morphisms]] [[!redirects proper scheme]] [[!redirects proper schemes]] [[!redirects proper morphism of schemes]] [[!redirects proper morphisms of schemes]] [[!redirects proper functor]] [[!redirects proper functors]] \end{document}