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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*{Gabriel localization} \hypertarget{contents}{}\section*{{Contents}}\label{contents} \noindent\hyperlink{idea}{Idea}\dotfill \pageref*{idea} \linebreak \noindent\hyperlink{related_entries}{Related entries}\dotfill \pageref*{related_entries} \linebreak \noindent\hyperlink{references}{References}\dotfill \pageref*{references} \linebreak \hypertarget{idea}{}\subsection*{{Idea}}\label{idea} [[Pierre Gabriel]] introduced a number of constructions in localization theory, mostly in [[abelian category|abelian]] context in his thesis published as \begin{itemize}% \item [[Pierre Gabriel]], [[Des Categories Abeliennes]] \end{itemize} and in general context in his [[Gabriel-Zisman|book]] with Zisman. By \textbf{Gabriel localization} one usually means a specific class of localizations of rings and the corresponding localization of categories of modules over rings. Given a (possibly noncommutative and nonunital) ring $R$ and a [[Gabriel filter]] $\mathcal{F}$ of left ideals in $R$, a Gabriel localization endofunctor \begin{displaymath} G_{\mathcal{F}} : {}_R Mod\to {}_R Mod \end{displaymath} is defined in one of the number of equivalent ways. For example, for any [[uniform filter]] $\mathcal{F}$ of left ideals in $R$ one defines a subfunctor of the identity functor $\sigma_{\mathcal{F}}$ on the category of left $R$-modules \begin{displaymath} M\mapsto \sigma_{\mathcal{F}}(M) = \sigma_{\mathcal{L}} = \{m\in M \,|\, m\in M, \exists m\in M,\, Jm = 0\}\subset M \end{displaymath} In a later work of Goldman $\sigma_{\mathcal{L}}$ was called a radical functor. If $\mathcal{F}$ is not only uniform but in fact a [[Gabriel filter]] then the radical $\sigma_{\mathcal{F}}$ is idempotent, i.e. $\sigma_{\mathcal{F}}^2 = \sigma_{\mathcal{F}}$. If $R$ is unital, $\sigma_{\mathcal{F}}$ is equivalent to the functor given on objects by \begin{displaymath} \sigma'_{\mathcal{L}}(M) = colim_{J\in\mathcal{F}} Hom_R(R/J,M) \end{displaymath} For each uniform fiter $\mathcal{F}$ one also defines the endofunctor $H_{\mathcal{F}}$ on ${}_R Mod$ by \begin{displaymath} H_{\mathcal{F}}(M) = colim_{J\in\mathcal{F}} Hom_R(J,M) \end{displaymath} (the colimit is over downward directed family of ;eft ideals in $\mathcal{F}$ and is a colimit of a functor with values in the category of abelian groups; the uniformness condition however gurantees that there is a canonical structure of an $R$-module on the colimit group $H_{\mathcal{F}}(M)$). Finally, for the Gabriel filter $\mathcal{F}$ one defines the Gabriel (endo)functor $G_{\mathcal{F}}$ on objects by \begin{displaymath} G_{\mathcal{F}}(M) := H_{\mathcal{F}}(M/\sigma_{\mathcal{F}}(M)) = colim_{J\in\mathcal{L}}Hom_R(J,M/\sigma_{\mathcal{F}}(M)) \end{displaymath} The essential image of the functor $G_{\mathcal{F}}$ is the localized category. The left $R$-module $G_{\mathcal{F}}(R)$ has a canonical structure of a ring over $R$; there is a natural forgetful functor from the localized category to the category of left $G_{\mathcal{F}}(R)$-modules. Under strong assumptions on the filter this functor is in fact an equivalence of categories, e.g. when the localization is [[Ore localization|Ore]]. \hypertarget{related_entries}{}\subsection*{{Related entries}}\label{related_entries} \begin{itemize}% \item \emph{[[Calculus of fractions and homotopy theory]]} \end{itemize} \hypertarget{references}{}\subsection*{{References}}\label{references} \begin{itemize}% \item [[Zoran Škoda]], \emph{Localizations for construction of quantum coset spaces}, in ``Noncommutative geometry and Quantum groups'', W.Pusz, P.M. Hajac, eds. Banach Center Publications vol.61, pp. 265--298, Warszawa 2003, \href{http://arxiv.org/abs/math.QA/0301090}{math.QA/0301090}. \item [[Zoran Škoda]], \emph{Noncommutative localization in noncommutative geometry}, London Math. Society Lecture Note Series \textbf{330}, ed. [[A. Ranicki]]; pp. 220--313, \href{http://arxiv.org/abs/math.QA/0403276}{math.QA/0403276} \end{itemize} \end{document}