\documentclass[12pt,titlepage]{article} \usepackage{amsmath} \usepackage{mathrsfs} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsthm} \usepackage{mathtools} \usepackage{graphicx} \usepackage{color} \usepackage{ucs} \usepackage[utf8x]{inputenc} \usepackage{xparse} \usepackage{hyperref} %----Macros---------- % % Unresolved issues: % % \righttoleftarrow % \lefttorightarrow % % \color{} with HTML colorspec % \bgcolor % \array with options (without options, it's equivalent to the matrix environment) % Of the standard HTML named colors, white, black, red, green, blue and yellow % are predefined in the color package. Here are the rest. \definecolor{aqua}{rgb}{0, 1.0, 1.0} \definecolor{fuschia}{rgb}{1.0, 0, 1.0} \definecolor{gray}{rgb}{0.502, 0.502, 0.502} \definecolor{lime}{rgb}{0, 1.0, 0} \definecolor{maroon}{rgb}{0.502, 0, 0} \definecolor{navy}{rgb}{0, 0, 0.502} \definecolor{olive}{rgb}{0.502, 0.502, 0} \definecolor{purple}{rgb}{0.502, 0, 0.502} \definecolor{silver}{rgb}{0.753, 0.753, 0.753} \definecolor{teal}{rgb}{0, 0.502, 0.502} % Because of conflicts, \space and \mathop are converted to % \itexspace and \operatorname during preprocessing. % itex: \space{ht}{dp}{wd} % % Height and baseline depth measurements are in units of tenths of an ex while % the width is measured in tenths of an em. \makeatletter \newdimen\itex@wd% \newdimen\itex@dp% \newdimen\itex@thd% \def\itexspace#1#2#3{\itex@wd=#3em% \itex@wd=0.1\itex@wd% \itex@dp=#2ex% \itex@dp=0.1\itex@dp% \itex@thd=#1ex% \itex@thd=0.1\itex@thd% \advance\itex@thd\the\itex@dp% \makebox[\the\itex@wd]{\rule[-\the\itex@dp]{0cm}{\the\itex@thd}}} \makeatother % \tensor and \multiscript \makeatletter \newif\if@sup \newtoks\@sups \def\append@sup#1{\edef\act{\noexpand\@sups={\the\@sups #1}}\act}% \def\reset@sup{\@supfalse\@sups={}}% \def\mk@scripts#1#2{\if #2/ \if@sup ^{\the\@sups}\fi \else% \ifx #1_ \if@sup ^{\the\@sups}\reset@sup \fi {}_{#2}% \else \append@sup#2 \@suptrue \fi% \expandafter\mk@scripts\fi} \def\tensor#1#2{\reset@sup#1\mk@scripts#2_/} \def\multiscripts#1#2#3{\reset@sup{}\mk@scripts#1_/#2% \reset@sup\mk@scripts#3_/} \makeatother % \slash \makeatletter \newbox\slashbox \setbox\slashbox=\hbox{$/$} \def\itex@pslash#1{\setbox\@tempboxa=\hbox{$#1$} \@tempdima=0.5\wd\slashbox \advance\@tempdima 0.5\wd\@tempboxa \copy\slashbox \kern-\@tempdima \box\@tempboxa} \def\slash{\protect\itex@pslash} \makeatother % math-mode versions of \rlap, etc % from Alexander Perlis, "A complement to \smash, \llap, and lap" % http://math.arizona.edu/~aprl/publications/mathclap/ \def\clap#1{\hbox to 0pt{\hss#1\hss}} \def\mathllap{\mathpalette\mathllapinternal} \def\mathrlap{\mathpalette\mathrlapinternal} \def\mathclap{\mathpalette\mathclapinternal} \def\mathllapinternal#1#2{\llap{$\mathsurround=0pt#1{#2}$}} \def\mathrlapinternal#1#2{\rlap{$\mathsurround=0pt#1{#2}$}} \def\mathclapinternal#1#2{\clap{$\mathsurround=0pt#1{#2}$}} % Renames \sqrt as \oldsqrt and redefine root to result in \sqrt[#1]{#2} \let\oldroot\root \def\root#1#2{\oldroot #1 \of{#2}} \renewcommand{\sqrt}[2][]{\oldroot #1 \of{#2}} % Manually declare the txfonts symbolsC font \DeclareSymbolFont{symbolsC}{U}{txsyc}{m}{n} \SetSymbolFont{symbolsC}{bold}{U}{txsyc}{bx}{n} \DeclareFontSubstitution{U}{txsyc}{m}{n} % Manually declare the stmaryrd font \DeclareSymbolFont{stmry}{U}{stmry}{m}{n} \SetSymbolFont{stmry}{bold}{U}{stmry}{b}{n} % Manually declare the MnSymbolE font \DeclareFontFamily{OMX}{MnSymbolE}{} \DeclareSymbolFont{mnomx}{OMX}{MnSymbolE}{m}{n} \SetSymbolFont{mnomx}{bold}{OMX}{MnSymbolE}{b}{n} \DeclareFontShape{OMX}{MnSymbolE}{m}{n}{ <-6> MnSymbolE5 <6-7> MnSymbolE6 <7-8> MnSymbolE7 <8-9> MnSymbolE8 <9-10> MnSymbolE9 <10-12> MnSymbolE10 <12-> MnSymbolE12}{} % Declare specific arrows from txfonts without loading the full package \makeatletter \def\re@DeclareMathSymbol#1#2#3#4{% \let#1=\undefined \DeclareMathSymbol{#1}{#2}{#3}{#4}} \re@DeclareMathSymbol{\neArrow}{\mathrel}{symbolsC}{116} \re@DeclareMathSymbol{\neArr}{\mathrel}{symbolsC}{116} \re@DeclareMathSymbol{\seArrow}{\mathrel}{symbolsC}{117} \re@DeclareMathSymbol{\seArr}{\mathrel}{symbolsC}{117} \re@DeclareMathSymbol{\nwArrow}{\mathrel}{symbolsC}{118} \re@DeclareMathSymbol{\nwArr}{\mathrel}{symbolsC}{118} \re@DeclareMathSymbol{\swArrow}{\mathrel}{symbolsC}{119} \re@DeclareMathSymbol{\swArr}{\mathrel}{symbolsC}{119} \re@DeclareMathSymbol{\nequiv}{\mathrel}{symbolsC}{46} \re@DeclareMathSymbol{\Perp}{\mathrel}{symbolsC}{121} \re@DeclareMathSymbol{\Vbar}{\mathrel}{symbolsC}{121} \re@DeclareMathSymbol{\sslash}{\mathrel}{stmry}{12} \re@DeclareMathSymbol{\bigsqcap}{\mathop}{stmry}{"64} \re@DeclareMathSymbol{\biginterleave}{\mathop}{stmry}{"6} \re@DeclareMathSymbol{\invamp}{\mathrel}{symbolsC}{77} \re@DeclareMathSymbol{\parr}{\mathrel}{symbolsC}{77} \makeatother % \llangle, \rrangle, \lmoustache and \rmoustache from MnSymbolE \makeatletter \def\Decl@Mn@Delim#1#2#3#4{% \if\relax\noexpand#1% \let#1\undefined \fi \DeclareMathDelimiter{#1}{#2}{#3}{#4}{#3}{#4}} \def\Decl@Mn@Open#1#2#3{\Decl@Mn@Delim{#1}{\mathopen}{#2}{#3}} \def\Decl@Mn@Close#1#2#3{\Decl@Mn@Delim{#1}{\mathclose}{#2}{#3}} \Decl@Mn@Open{\llangle}{mnomx}{'164} \Decl@Mn@Close{\rrangle}{mnomx}{'171} \Decl@Mn@Open{\lmoustache}{mnomx}{'245} \Decl@Mn@Close{\rmoustache}{mnomx}{'244} \makeatother % Widecheck \makeatletter \DeclareRobustCommand\widecheck[1]{{\mathpalette\@widecheck{#1}}} \def\@widecheck#1#2{% \setbox\z@\hbox{\m@th$#1#2$}% \setbox\tw@\hbox{\m@th$#1% \widehat{% \vrule\@width\z@\@height\ht\z@ \vrule\@height\z@\@width\wd\z@}$}% \dp\tw@-\ht\z@ \@tempdima\ht\z@ \advance\@tempdima2\ht\tw@ \divide\@tempdima\thr@@ \setbox\tw@\hbox{% \raise\@tempdima\hbox{\scalebox{1}[-1]{\lower\@tempdima\box \tw@}}}% {\ooalign{\box\tw@ \cr \box\z@}}} \makeatother % \mathraisebox{voffset}[height][depth]{something} \makeatletter \NewDocumentCommand\mathraisebox{moom}{% \IfNoValueTF{#2}{\def\@temp##1##2{\raisebox{#1}{$\m@th##1##2$}}}{% \IfNoValueTF{#3}{\def\@temp##1##2{\raisebox{#1}[#2]{$\m@th##1##2$}}% }{\def\@temp##1##2{\raisebox{#1}[#2][#3]{$\m@th##1##2$}}}}% \mathpalette\@temp{#4}} \makeatletter % udots (taken from yhmath) \makeatletter \def\udots{\mathinner{\mkern2mu\raise\p@\hbox{.} \mkern2mu\raise4\p@\hbox{.}\mkern1mu \raise7\p@\vbox{\kern7\p@\hbox{.}}\mkern1mu}} \makeatother %% Fix array \newcommand{\itexarray}[1]{\begin{matrix}#1\end{matrix}} %% \itexnum is a noop \newcommand{\itexnum}[1]{#1} %% Renaming existing commands \newcommand{\underoverset}[3]{\underset{#1}{\overset{#2}{#3}}} \newcommand{\widevec}{\overrightarrow} \newcommand{\darr}{\downarrow} \newcommand{\nearr}{\nearrow} \newcommand{\nwarr}{\nwarrow} \newcommand{\searr}{\searrow} \newcommand{\swarr}{\swarrow} \newcommand{\curvearrowbotright}{\curvearrowright} \newcommand{\uparr}{\uparrow} \newcommand{\downuparrow}{\updownarrow} \newcommand{\duparr}{\updownarrow} \newcommand{\updarr}{\updownarrow} \newcommand{\gt}{>} \newcommand{\lt}{<} \newcommand{\map}{\mapsto} \newcommand{\embedsin}{\hookrightarrow} \newcommand{\Alpha}{A} \newcommand{\Beta}{B} \newcommand{\Zeta}{Z} \newcommand{\Eta}{H} \newcommand{\Iota}{I} \newcommand{\Kappa}{K} \newcommand{\Mu}{M} \newcommand{\Nu}{N} \newcommand{\Rho}{P} \newcommand{\Tau}{T} \newcommand{\Upsi}{\Upsilon} \newcommand{\omicron}{o} \newcommand{\lang}{\langle} \newcommand{\rang}{\rangle} \newcommand{\Union}{\bigcup} \newcommand{\Intersection}{\bigcap} \newcommand{\Oplus}{\bigoplus} \newcommand{\Otimes}{\bigotimes} \newcommand{\Wedge}{\bigwedge} \newcommand{\Vee}{\bigvee} \newcommand{\coproduct}{\coprod} \newcommand{\product}{\prod} \newcommand{\closure}{\overline} \newcommand{\integral}{\int} \newcommand{\doubleintegral}{\iint} \newcommand{\tripleintegral}{\iiint} \newcommand{\quadrupleintegral}{\iiiint} \newcommand{\conint}{\oint} \newcommand{\contourintegral}{\oint} \newcommand{\infinity}{\infty} \newcommand{\bottom}{\bot} \newcommand{\minusb}{\boxminus} \newcommand{\plusb}{\boxplus} \newcommand{\timesb}{\boxtimes} \newcommand{\intersection}{\cap} \newcommand{\union}{\cup} \newcommand{\Del}{\nabla} \newcommand{\odash}{\circleddash} \newcommand{\negspace}{\!} \newcommand{\widebar}{\overline} \newcommand{\textsize}{\normalsize} \renewcommand{\scriptsize}{\scriptstyle} \newcommand{\scriptscriptsize}{\scriptscriptstyle} \newcommand{\mathfr}{\mathfrak} \newcommand{\statusline}[2]{#2} \newcommand{\tooltip}[2]{#2} \newcommand{\toggle}[2]{#2} % Theorem Environments \theoremstyle{plain} \newtheorem{theorem}{Theorem} \newtheorem{lemma}{Lemma} \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*{Bousfield localization of spectra} \hypertarget{context}{}\subsubsection*{{Context}}\label{context} \hypertarget{cohomology}{}\paragraph*{{Cohomology}}\label{cohomology} [[!include cohomology - contents]] \hypertarget{stable_homotopy_theory}{}\paragraph*{{Stable Homotopy theory}}\label{stable_homotopy_theory} [[!include stable homotopy theory - contents]] \hypertarget{higher_algebra}{}\paragraph*{{Higher algebra}}\label{higher_algebra} [[!include higher algebra - 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{properties}{Properties}\dotfill \pageref*{properties} \linebreak \noindent\hyperlink{localization_at_moore_spectra_of_abelian_groups}{Localization at Moore spectra of abelian groups}\dotfill \pageref*{localization_at_moore_spectra_of_abelian_groups} \linebreak \noindent\hyperlink{relation_to_nilpotent_completion}{Relation to nilpotent completion}\dotfill \pageref*{relation_to_nilpotent_completion} \linebreak \noindent\hyperlink{fracture_theorem}{Fracture theorem}\dotfill \pageref*{fracture_theorem} \linebreak \noindent\hyperlink{examples}{Examples}\dotfill \pageref*{examples} \linebreak \noindent\hyperlink{general}{General}\dotfill \pageref*{general} \linebreak \noindent\hyperlink{rationalization}{Rationalization}\dotfill \pageref*{rationalization} \linebreak \noindent\hyperlink{localization}{$p$-Localization}\dotfill \pageref*{localization} \linebreak \noindent\hyperlink{completion}{$p$-Completion}\dotfill \pageref*{completion} \linebreak \noindent\hyperlink{telescopic_localization}{Telescopic localization}\dotfill \pageref*{telescopic_localization} \linebreak \noindent\hyperlink{chromatic_localization}{Chromatic localization}\dotfill \pageref*{chromatic_localization} \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} \emph{Bousfield localization of spectra} refers generally to [[localization of an (∞,1)-category|localizations]] of the [[stable (∞,1)-category of spectra]] (hence [[Bousfield localization of model categories|Bousfield localization]] of [[model categories of spectra]]) at the collection of [[morphisms]] which become [[equivalences]] under [[smash product of spectra|smash product]] with a given [[spectrum]] $E$. Since any such $E$ represents a [[generalized homology theory]], this may also be thought of \emph{$E$-[[homology localization]]}. More specifically, if the [[stable (∞,1)-category of spectra]] is [[presentable (infinity,1)-category|presented]] by a ([[stable model category|stable]]) [[model category]], then the [[localization of an (∞,1)-category|∞-categorical localization]] can be presented by the operation of \emph{[[Bousfield localization of model categories]]}. The original article (\hyperlink{Bousfield79}{Bousfield 79}) essentially considered localization at the level of [[homotopy categories]]. Specifically, for $E \in Spec$ a [[spectrum]], the \emph{Bousfield localization at $E$} of another [[spectrum]] $X$ is the [[universal property|universal map]] \begin{displaymath} X \longrightarrow L_E X \end{displaymath} to the \emph{$E$-[[local spectrum]]} $L_E X$, with the property that for $Y$ any $E$-acyclic spectrum in that $Y \wedge E \simeq 0$, every morphism $Y \longrightarrow L_E X$ is null-homotopic (a [[zero morphism]] in the [[stable (∞,1)-category of spectra]]). (see for instance \hyperlink{Lurie10}{Lurie 10, Example 4}) For $E = M \mathbb{Z}_p$ the [[Moore spectrum]] of the [[cyclic group]] $\mathbb{Z}_p \coloneqq \mathbb{Z}/p\mathbb{Z}$ for some [[prime number]] $p$, this $E$-localization is \emph{[[p-completion]]}. (see for instance \hyperlink{Lurie10}{Lurie 10, Examples 7 and 8}) \hypertarget{definition}{}\subsection*{{Definition}}\label{definition} We write $Ho(Spectra)$ for the [[stable homotopy category]]. For $X,Y \in Ho(Spectra)$ two [[spectra]] we write $[X,Y] \in$ [[Ab]] for its [[hom-object|hom-]][[abelian groups]], and $[X,Y]_\bullet \coloneqq [\Sigma^\bullet X,Y]$ for the corresponding [[graded abelian group]] (\href{Introduction+to+Stable+homotopy+theory+--+1-1#GradedAbelianGroupStructureOnHomsInTheHomotopyCategory}{def.}). \begin{defn} \label{EAcyclicAndLocalSpectra}\hypertarget{EAcyclicAndLocalSpectra}{} Let $E \in Ho(Spectra)$ be a [[spectrum]]. Say that \begin{enumerate}% \item a spectrum $X$ is \textbf{$E$-acyclic} if the [[smash product of spectra|smash product]] with $E$ is [[zero object|zero]], $E \wedge X \simeq 0$; \item a morphism $f \colon X \to Y$ of spectra is an \textbf{$E$-equivalence} if $E \wedge f \;\colon\; E \wedge X \to E \wedge Y$ is an [[isomorphism]] in $Ho(Spectra)$, hence if $E_\bullet(f)$ is an isomorphism in $E$-[[generalized homology]]; \item a spectrum $X$ is \textbf{$E$-local} if the following equivalent conditions hold \begin{enumerate}% \item for every $E$-equivalence $f$ then $[f,X]_\bullet$ is an isomorphism; \item every [[morphism]] $Y \longrightarrow X$ out of an $E$-acyclic spectrum $Y$ is [[zero morphism|zero]] in $Ho(Spectra)$; \end{enumerate} \end{enumerate} \end{defn} (\hyperlink{Bousfield79}{Bousfield 79, \S{}1}) see also for instance (\hyperlink{Lurie10}{Lurie, Lecture 20, example 4}) \begin{lemma} \label{TwoConditionsOnELocalSpectrumAreEquivalent}\hypertarget{TwoConditionsOnELocalSpectrumAreEquivalent}{} The two conditions in the last item of def. \ref{EAcyclicAndLocalSpectra} are indeed equivalent. \end{lemma} \begin{proof} Notice that $A \in Ho(Spectra)$ being $E$-acyclic means equivalently that the unique morphism $0 \longrightarrow A$ is an $E$-equivalence. Hence one direction of the claim is trivial. For the other direction we need to show that for $[-,X]_\bullet$ to give an isomorphism on all $E$-equivalences $f$, it is sufficient that it gives an isomorphism on all $E$-equivalences of the form $0 \to A$. Given a morphism $f \colon A \to B$, write $B \longrightarrow B/A$ for its [[homotopy cofiber]]. Then since $Ho(Spectra)$ is a [[triangulated category]] (\href{Introduction+to+Stable+homotopy+theory+--+1-1#StableHomotopyCategoryIsTriangulated}{prop.}) the defining axioms of triangulated categories (\href{Introduction+to+Stable+homotopy+theory+--+1-1#CategoryWithCofiberSequences}{def.}, \href{Introduction+to+Stable+homotopy+theory+--+1-1#TrianglesMayBeShiftedToTheLeft}{lemma}) give that there is a [[commuting diagram]] of the form \begin{displaymath} \itexarray{ 0 &\longrightarrow& A &\overset{id}{\longrightarrow}& A &\overset{}{\longrightarrow}& 0 &\overset{}{\longrightarrow}& \Sigma A \\ \downarrow && \downarrow^{\mathrlap{id}} && \downarrow^{\mathrlap{f}} && \downarrow && \downarrow^{\mathrlap{id}} \\ \Sigma^{-1} B/A &\longrightarrow& A &\underset{f}{\longrightarrow}& B &\longrightarrow& B/A &\longrightarrow& \Sigma A } \,, \end{displaymath} where both the top as well as the bottom are [[homotopy cofiber sequences]]. Hence applying $[-,X]_\bullet$ to this diagram in $Ho(Spectra)$ yields a diagram of [[graded abelian groups]] of the form \begin{displaymath} \itexarray{ 0 &\longleftarrow& [A,X]_\bullet &\longleftarrow& [A,X]_\bullet &\longleftarrow& 0 &\longleftarrow& [A,X]_{\bullet+1} \\ \uparrow && \uparrow^{\mathrlap{id}} && \uparrow^{\mathrlap{[f,X]_\bullet}} && \uparrow && \uparrow^{\mathrlap{id}} \\ [B/A,X]_{\bullet+1} &\longleftarrow& [A,X]_\bullet &\longleftarrow& [B,X]_\bullet &\longleftarrow& [B/A,X]_\bullet &\longleftarrow& [A,X]_{\bullet+1} } \,, \end{displaymath} where now both horizontal sequences are [[long exact sequences]] (\href{Introduction+to+Stable+homotopy+theory+--+1-1#LongFiberSequencesOfMapsOfSpectra}{prop.}). Hence if $[B/A,X]_\bullet \longrightarrow 0$ is an isomorphism, then all four outer vertical morphisms in this diagram are isomorphisms, and then the [[five-lemma]] implies that also $[f,X]_\bullet$ is an isomorphism. Hence it is now sufficient to observe that with $f \colon A \to B$ an $E$-equivalence, then its homotopy cofiber $B/A$ is $E$-acyclic. To see this, notice that by the [[tensor triangulated category|tensor triangulated]] structure on $Ho(Spectra)$ (\href{Introduction+to+Stable+homotopy+theory+--+1-2#TensorTriangulatedStructureOnStableHomotopyCategory}{prop.}) the [[smash product of spectra|smash product]] with $E$ preserves homotopy cofiber sequences, so that there is a homotopy cofiber sequence \begin{displaymath} E \wedge A \overset{E \wedge f}{\longrightarrow} E \wedge B \longrightarrow E \wedge (B/A) \longrightarrow E \wedge \Sigma A \,. \end{displaymath} But if the first morphism here is an isomorphism, then the axioms of a [[triangulated category]] (\href{Introduction+to+Stable+homotopy+theory+--+1-1#CategoryWithCofiberSequences}{def.}) imply that $E \wedge B / A \simeq 0$. In detail: by the axioms we may form the morphism of homotopy cofiber sequences \begin{displaymath} \itexarray{ E \wedge A &\overset{E \wedge f}{\longrightarrow}& E \wedge B &\longrightarrow& E \wedge B/A &\longrightarrow& E \wedge \Sigma A \\ \downarrow^{\mathrlap{id}} && \downarrow^{\mathrlap{(E\wedge f)^{-1}}} && \downarrow && \downarrow^{\mathrlap{id}} \\ E \wedge A &\underset{id}{\longrightarrow}& E \wedge A &\longrightarrow& 0 &\longrightarrow& E \wedge \Sigma A } \,. \end{displaymath} Then since two of the three vertical morphisms on the left are isomorphisms, so is the third (\href{Introduction+to+Stable+homotopy+theory+--+1-1#TwoOutOfThreeForMorphismsOfDistinguishedTriangles}{lemma}). \end{proof} \begin{defn} \label{ELocalizationOfSpectra}\hypertarget{ELocalizationOfSpectra}{} Given $E,X \in Ho(Spectra)$, then an \textbf{$E$-localization} of $X$ is \begin{enumerate}% \item an $E$-local spectrum $L_E X$ \item an $E$-equivalence $X \longrightarrow L_E X$. \end{enumerate} according to def. \ref{EAcyclicAndLocalSpectra}. \end{defn} We discuss now that $E$-Localizations always exist. The key to this is the following lemma \ref{KappaCellSpectrumWitnessingELocalization}, which asserts that a spectrum being $E$-local is equivalent to it being $A$-null, for some ``small'' spectrum $A$: \begin{lemma} \label{KappaCellSpectrumWitnessingELocalization}\hypertarget{KappaCellSpectrumWitnessingELocalization}{} For every [[spectrum]] $E$ there exists a spectrum $A$ such that any spectrum $X$ is $E$-local (def. \ref{EAcyclicAndLocalSpectra}) precisely if it is $A$-null, i.e. \begin{displaymath} X \;is\; E\text{-local} \;\;\;\; \Leftrightarrow \;\;\;\; [A,X]_\ast = 0 \end{displaymath} and such that \begin{enumerate}% \item $A$ is $E$-acyclic (def. \ref{EAcyclicAndLocalSpectra}); \item there exists an infinite [[cardinal number]] $\kappa$ such that $A$ is a $\kappa$-[[CW spectrum]] (hence a [[CW spectrum]] (\href{Introduction+to+Stable+homotopy+theory+--+1-1#CWSpectrum}{def.}) with at most $\kappa$ many cells); \item the class of $E$-acyclic spectra (def. \ref{EAcyclicAndLocalSpectra}) is the class generated by $A$ under \begin{enumerate}% \item [[wedge sum]] \item the relation that if in a [[homotopy cofiber sequence]] $X_1 \to X_2 \to X_3$ two of the spectra are in the class, then so is the third. \end{enumerate} \end{enumerate} \end{lemma} (\hyperlink{Bousfield79}{Bousfield 79, lemma 1.13 with lemma 1.14}) review includes (\href{Bauer11}{Bauer 11, p.2,3}, \hyperlink{VanKoughnett13}{VanKoughnett 13, p. 8}) \begin{prop} \label{ELocalizationCofiber}\hypertarget{ELocalizationCofiber}{} For $E \in Ho(Spectra)$ any [[spectrum]], every spectrum $X$ sits in a [[homotopy cofiber sequence]] of the form \begin{displaymath} G_E(X) \longrightarrow X \overset{\eta_X}{\longrightarrow} L_E(X) \,, \end{displaymath} and [[natural transformation|natural]] in $X$, such that \begin{enumerate}% \item $G_E(X)$ is $E$-acyclic, \item $L_E(X)$ is $E$-local, \end{enumerate} according to def. \ref{EAcyclicAndLocalSpectra}. \end{prop} (\hyperlink{Bousfield79}{Bousfield 79, theorem 1.1}) see also for instance (\hyperlink{Lurie10}{Lurie, Lecture 20, example 4}) \begin{proof} Consider the $\kappa$-[[CW-spectrum]] spectrum $A$ whose existence is asserted by lemma \ref{KappaCellSpectrumWitnessingELocalization}. Let \begin{displaymath} I_A \coloneqq \{A \to Cone(A)\} \end{displaymath} denote the set containing as its single element the canonical morphism (of [[sequential spectra]]) from $A$ into the standard [[cone]] of $A$, i.e. the cofiber \begin{displaymath} Cone(A) \coloneqq cofib( A \to A \wedge I_+ ) \simeq A \wedge I \end{displaymath} of the inclusion of $A$ into its standard [[cylinder spectrum]] (\href{Introduction+to+Stable+homotopy+theory+--+1-1#StandardCylinderSpectrumSequential}{def.}). Since the standard cylinder spectrum on a CW-spectrum is a [[good cylinder object]] (\href{Introduction+to+Stable+homotopy+theory+--+1-1#CylinderSpectrumOverCWSpectrumIsGood}{prop.}) this means (\href{Introduction+to+Stable+homotopy+theory+--+P#HomsOutOfCofibrantIntoFibrantComputeHomotopyCategory}{lemma}) that for $X$ any fibrant sequential spectrum, and for $A \longrightarrow X$ any morphism, then an extension along the cone inclusion \begin{displaymath} \itexarray{ A &\longrightarrow& X \\ \downarrow & \nearrow \\ Cone(A) } \end{displaymath} equivalently exhibits a null-homotopy of the top morphism. Hence the $(A \to Cone(A))$-[[injective objects]] in $Ho(Spectra)$ are precisely those spectra $X$ for which $[A,X]_\bullet \simeq 0$. Moreover, due to the degreewise nature of the smash tensoring $Cone(A) = A \wedge I$ (\href{Introduction+to+Stable+homotopy+theory+--+1-1#TensoringAndPoweringOfSequentialSpectra}{def}), the inclusion morphism $A \to Cone(A)$ is degreewise the inclusion of a [[CW-complex]] into its standard cone, which is a [[relative cell complex]] inclusion (\href{Introduction+to+Stable+homotopy+theory+--+P#TopologicalCylinderOnCWComplexIsGoodCylinderObject}{prop.}). By \href{Introduction+to+Stable+homotopy+theory+--+1-1#kappaCellSpectrumIsKappaSmall}{this lemma} the $\kappa$-[[cell spectrum]] $A$ is \emph{$\kappa$-small object} (\href{Introduction+to+Stable+homotopy+theory+--+P#ClassOfMorphismsWithSmallDomains}{def.}) with respect to morphisms of spectra which are degreewise [[relative cell complex]] inclusion [[small object argument]] . Hence the [[small object argument]] applies (\href{Introduction+to+Stable+homotopy+theory+--+P#SmallObjectArgument}{prop.}) and gives for every $X$ a factorization of the terminal morphism $X \to \ast$ as an $I_A$-[[relative cell complex]] (\href{Introduction+to+Stable+homotopy+theory+--+P#TopologicalCCellComplex}{def.}) followed by an $I_A$-[[injective morphism]] (\href{Introduction+to+Stable+homotopy+theory+--+P#RightLiftingProperty}{def.}) \begin{displaymath} X \overset{I_A Cell}{\longrightarrow} L_E X \overset{I_A Inj}{\longrightarrow} \ast \,. \end{displaymath} By the above, this means that $[A, L_E X] = 0$, hence by lemma \ref{KappaCellSpectrumWitnessingELocalization} that $L_E X$ is $E$-local. It remains to see that the [[homotopy fiber]] of $X \to L_E X$ is $E$-acyclic: By the [[tensor triangulated category|tensor triangulated]] structure on $Ho(Spectra)$ (\href{Introduction+to+Stable+homotopy+theory+--+1-2#TensorTriangulatedStructureOnStableHomotopyCategory}{prop.}) it is sufficient to show that the [[homotopy cofiber]] is $E$-acyclic (since it differs from the homotopy fiber only by suspension). By the [[pasting law]], the homotopy cofiber of a [[transfinite composition]] is the transfinite composition of a sequence of homotopy pushouts. By lemma \ref{KappaCellSpectrumWitnessingELocalization} and applying the pasting law again, all these homotopy pushouts produce $E$-acyclic objects. Hence we conclude by observing that the the transfinite composition of the morphisms between these $E$-acyclic objects is $E$-acyclic. Since by construction all these morphisms are relative cell complex inclusions, this follows again with the compactness of the $n$-spheres (\href{Introduction+to+Stable+homotopy+theory+--+P#CompactSubsetsAreSmallInCellComplexes}{lemma}). \end{proof} \begin{lemma} \label{}\hypertarget{}{} The morphism $X \to L_E (X)$ in prop. \ref{ELocalizationCofiber} exhibits an $E$-localization of $X$ according to def. \ref{ELocalizationOfSpectra} \end{lemma} \begin{proof} It only remains to show that $X \to L_E X$ is an $E$-equivalence. By the [[tensor triangulated category|tensor triangulated]] structure on $Ho(Spectra)$ (\href{Introduction+to+Stable+homotopy+theory+--+1-2#TensorTriangulatedStructureOnStableHomotopyCategory}{prop.}) the [[smash product of spectra|smash product]] with $E$ preserves homotopy cofiber sequences, so that \begin{displaymath} E \wedge G_E X \longrightarrow E \wedge X \overset{E \wedge \eta_X}{\longrightarrow} E \wedge L_E X \longrightarrow E \wedge \Sigma G_E X \end{displaymath} is also a homotopy cofiber sequence. But now $E \wedge G_E X \simeq 0$ by prop. \ref{ELocalizationCofiber}, and so the axioms (\href{Introduction+to+Stable+homotopy+theory+--+1-1#CategoryWithCofiberSequences}{def.}) of the [[triangulated category|triangulated structure]] on $Ho(Spectra)$ (\href{Introduction+to+Stable+homotopy+theory+--+1-1#StableHomotopyCategoryIsTriangulated}{prop.}) imply that $E \wedge \eta$ is an isomorphism. \end{proof} \begin{remark} \label{Acyclification}\hypertarget{Acyclification}{} Hence where $L_E$ is traditionally called ``$E$-localization'', $G_E$ might be called ``$E$-acyclification'', though that terminology is not used commonly. \end{remark} \hypertarget{properties}{}\subsection*{{Properties}}\label{properties} \hypertarget{localization_at_moore_spectra_of_abelian_groups}{}\subsubsection*{{Localization at Moore spectra of abelian groups}}\label{localization_at_moore_spectra_of_abelian_groups} A basic special case of $E$-localization of spectra is given for $E = S A$ the [[Moore spectrum]] of an [[abelian group]] $A$ (\hyperlink{Bousfield79}{Bousfield 79, section 2}). For $A = \mathbb{Z}_{(p)}$ this is [[p-localization]] and for $A = \mathbb{F}_p$ this is [[p-completion]], see examples \ref{pLocalization} and \ref{pCompletion} below for more. \begin{prop} \label{}\hypertarget{}{} For $A_1$ and $A_2$ two [[abelian groups]] then the following are equivalent \begin{enumerate}% \item the Bousfield localizations at their [[Moore spectra]] are equivalent \begin{displaymath} L_{S A_1} \simeq L_{S A_2} \,; \end{displaymath} \item $A_1$ and $A_2$ have the same \emph{type of acyclicity}, meaning that \begin{enumerate}% \item every [[prime number]] $p$ is invertible in $A_1$ precisely if it is in $A_2$; \item $A_1$ is a [[torsion group]] precisely if $A_2$ is. \end{enumerate} \end{enumerate} \end{prop} (\hyperlink{Bousfield79}{Bousfield 79, prop. 2.3}) recalled e.g. in (\hyperlink{VanKoughnett13}{VanKoughnett 13, prop. 4.2}). This means that given an abelian group $A$ then \begin{itemize}% \item either $A$ is not torsion, then \begin{displaymath} L_{S A} \simeq L_{S \mathbb{Z}[I^{-1}]} \,, \end{displaymath} where $I$ is the set of primes invertible in $A$ and $\mathbb{Z}[I^{-1}] \hookrightarrow \mathbb{Q}$ is the [[localization of a ring|localization]] at these primes of the [[integers]]; \item or $A$ is torsion, then \begin{displaymath} L_{S A }\simeq L_{S(\oplus_q \mathbb{F}_q ) } \,, \end{displaymath} where the [[direct sum]] is over all [[cyclic groups]] of order $q$, for $q$ a prime not invertible in $A$. \end{itemize} \hypertarget{relation_to_nilpotent_completion}{}\subsubsection*{{Relation to nilpotent completion}}\label{relation_to_nilpotent_completion} Let $E$ be an [[E-∞ ring]] and let $X$ be any [[spectrum]] \begin{remark} \label{CanonicalMapFromELocalizationToTotalization}\hypertarget{CanonicalMapFromELocalizationToTotalization}{} There is a canonical map \begin{displaymath} L_E X \stackrel{}{\longrightarrow} \underset{\leftarrow}{\lim}_n (E^{\wedge^{n+1}_S}\wedge_S X) \end{displaymath} from the $E$-[[Bousfield localization of spectra]] of $X$ into the [[totalization]] of the canonical [[cosimplicial object|cosimplicial]] [[spectrum]] (see at \emph{[[nilpotent completion]]}). \end{remark} We now consider conditions for this morphism to be an [[equivalence]]. \begin{defn} \label{CoreOfARing}\hypertarget{CoreOfARing}{} For $R$ a [[ring]], its \emph{core} $c R$ is the [[equalizer]] in \begin{displaymath} c R \longrightarrow R \stackrel{\longrightarrow}{\longrightarrow} R \otimes R \,. \end{displaymath} \end{defn} \begin{prop} \label{SufficientConditionsForTotalizationToBeELocalization}\hypertarget{SufficientConditionsForTotalizationToBeELocalization}{} Let $E$ be a [[connective spectrum|connective]] [[E-∞ ring]] such that the core of $\pi_0(E)$, def. \ref{CoreOfARing}, is either of \begin{itemize}% \item the [[localization of a ring|localization]] of the [[integers]] at a set $J$ of [[primes]], $c \pi_0(E) \simeq \mathbb{Z}[J^{-1}]$; \item $\mathbb{Z}_n$ for $n \geq 2$. \end{itemize} Then the map in remark \ref{CanonicalMapFromELocalizationToTotalization} is an equivalence \begin{displaymath} L_E X \stackrel{\simeq}{\longrightarrow} \underset{\leftarrow}{\lim}_n (E^{\wedge^{n+1}_S}\wedge_S X) \,. \end{displaymath} \end{prop} (\hyperlink{Bousfield79}{Bousfield 79}) see also for instance (\hyperlink{Bauer11}{Bauer 11, p.2}) For more discussion of [[E-infinity geometry|E-infinity]] (derived) [[formal completions]] via totalizations of [[Amitsur complexes]], see (\href{completion+of+a+module#Carlsson07}{Carlsson 07}). \hypertarget{fracture_theorem}{}\subsubsection*{{Fracture theorem}}\label{fracture_theorem} The [[fracture theorem]] says how Bousfield localization at a [[coproduct]]/[[wedge sum]] of spectra is a [[homotopy pullback]] of Bousfield localization separately. See at \emph{[[fracture theorem]]} for more on this. \hypertarget{examples}{}\subsection*{{Examples}}\label{examples} \hypertarget{general}{}\subsubsection*{{General}}\label{general} \begin{example} \label{EModulesAreELocal}\hypertarget{EModulesAreELocal}{} For $E$ an [[E-∞ ring]], every [[∞-module]] $X$ over $E$ is $E$-local, def. \ref{EAcyclicAndLocalSpectra}. \end{example} (e.g. \hyperlink{Lurie10}{Lurie, Lecture 20, example 5}) \begin{example} \label{}\hypertarget{}{} For $E$ an [[E-∞ algebra]] over an [[E-∞ ring]] $S$ and for $X$ an $S$-[[∞-module]], consider the dual [[Cech nerve]] [[cosimplicial object]] \begin{displaymath} E^{\wedge_S^{\bullet+1}}\wedge_S X \;\colon\; \Delta \longrightarrow Spectra \,. \end{displaymath} By example \ref{EModulesAreELocal} each term is $E$-local, so that the map to the [[totalization]] \begin{displaymath} X \longrightarrow \underset{\leftarrow}{\lim} E^{\wedge_S^{\bullet+1}} \wedge_S X \end{displaymath} factors through the $E$-localization of $X$ \begin{displaymath} X \longrightarrow L_E X \longrightarrow \underset{\leftarrow}{\lim} E^{\wedge_S^{\bullet+1}} \wedge_S X \,. \end{displaymath} Under suitable condition the second map here is indeed an [[equivalence]], in which case the [[totalization]] of the dual [[Cech nerve]] exhibits the $E$-localization. This happens for instance in the discussion of the [[Adams spectral sequence]], see the examples given there. (see also e.g. \hyperlink{Bauer11}{Bauer 11, p. 2}) \end{example} \hypertarget{rationalization}{}\subsubsection*{{Rationalization}}\label{rationalization} \begin{example} \label{Rationalization}\hypertarget{Rationalization}{} Bousfield localization at the [[Moore spectrum]]/[[Eilenberg-MacLane spectrum]] $S \mathbb{Q}\simeq H\mathbb{Q}$ of the [[rational numbers]] is [[rationalization]] to [[rational homotopy theory]]. The corresponding $\mathbb{Q}$-acyclification (remark \ref{Acyclification}) is \emph{[[torsion approximation]]}. \end{example} e.g. (\hyperlink{Bauer11}{Bauer 11, example 1.7}) \hypertarget{localization}{}\subsubsection*{{$p$-Localization}}\label{localization} For $p$ a [[prime number]] write $\mathbb{Z}_{(p)}$ for the [[localization of a ring|localization]] of the [[integers]] \emph{at} $(p)$, for the ring of integers [[localization of a ring|localized at]] $p$, hence with all primes \emph{except} $p$ inverted; equivalently the subring of the [[rational numbers]] with denominator not divisible by $p$. \begin{example} \label{pLocalization}\hypertarget{pLocalization}{} The Bousfield localization at the [[Moore spectrum]] $S \mathbb{Z}_{(p)}$ is [[p-localization]]. \end{example} (\hyperlink{Bousfield79}{Bousfield 79}), \hyperlink{Bauer11}{Bauer 11, example 1.7}). See at \emph{[[localization of a space]]} for details on this. \begin{prop} \label{pLocalizationIsSmashing}\hypertarget{pLocalizationIsSmashing}{} $p$-localization is a [[smashing localization]]: \begin{displaymath} L_{S \mathbb{Z}_{(p)}} X \simeq S \mathbb{Z}_{(p)} \wedge X \,. \end{displaymath} \end{prop} (\hyperlink{Bousfield79}{Bousfield 79, prop. 2.4}) recalled e.g. as (\hyperlink{VanKoughnett13}{van Koughnett 13, prop. 4.3}). \hypertarget{completion}{}\subsubsection*{{$p$-Completion}}\label{completion} For $p \in \mathbb{N}$ a [[prime number]], write \begin{displaymath} \mathbb{F}_p = \mathbb{Z}/(p) \end{displaymath} for the [[cyclic group]]/[[finite field]] of [[order of a group|order]] $p$. \begin{defn} \label{}\hypertarget{}{} Write \begin{displaymath} \mathbb{Z}/p^\infty \coloneqq (\mathbb{Z}[p^{-1}])/\mathbb{Z} \end{displaymath} for the [[localization of a ring|localization]] of the [[integers]] away from $p$ followed by the quotient by $\mathbb{Z}$. \end{defn} e.g. (\hyperlink{Bousfield79}{Bousfield 79, p. 6}) \begin{remark} \label{}\hypertarget{}{} The [[short exact sequence]] of [[abelian groups]] \begin{displaymath} 0 \to \mathbb{Z} \longrightarrow \mathbb{Z}[p^{-1}] \longrightarrow \mathbb{Z}/p^\infty \to 0 \end{displaymath} induces the [[homotopy fiber sequence]] (in [[spectra]]) of [[Moore spectra]] \begin{displaymath} \Omega S(\mathbb{Z}/p^\infty) \longrightarrow S\mathbb{Z} \longrightarrow S(\mathbb{Z}[p^{-1}]) \,. \end{displaymath} As in \hyperlink{Bousfield79}{Bousfield 79, p. 6} one also writes \begin{displaymath} S^{-1} (\mathbb{Z}/p^\infty) \coloneqq \Omega S(\mathbb{Z}/p^\infty) \,. \end{displaymath} \end{remark} \begin{prop} \label{}\hypertarget{}{} The localization of spectra at the [[Moore spectrum]] $S\mathbb{F}_p$ is given by the [[mapping spectrum]] out of $S^{-1} \mathbb{Z}/p^\infty$: \begin{displaymath} L_{S \mathbb{F}_p} X \simeq [\Omega S \mathbb{Z}/p^\infty, X] \,. \end{displaymath} \end{prop} (\hyperlink{Bousfield79}{Bousfield 79, prop. 2.5}) Fact: $\mathbb{F}_p$-localizaton is [[p-completion]], e.g. \hyperlink{LurieProper}{Lurie ``Proper Morphisms\ldots{}'', section 4}. \begin{example} \label{}\hypertarget{}{} Let \begin{displaymath} E \coloneqq H \mathbb{Z}/p\mathbb{Z} \end{displaymath} be the corresponding [[Moore spectrum]]. Then a spectrum which corresponds to a [[chain complex]] under the \href{module+spectrum#StableDoldKanCorrespondence}{stable Dold-Kan corespondence} is $E$-local, def. \ref{AcyclicAndLocal}, if that chain complex has [[chain homology]] groups being $\mathbb{Z}[p^{-1}]$-modules. The $E$-localization of a spectrum in this case is \emph{[[p-completion]]}. \end{example} (e.g. \hyperlink{Lurie10}{Lurie, Lecture 20, example 8}) More generally \begin{example} \label{pCompletion}\hypertarget{pCompletion}{} Bousfield localization at the [[Moore spectrum]] $S \mathbb{F}_p$ is [[p-completion]] to [[p-adic homotopy theory]]. \end{example} E.g. (\hyperlink{Bauer11}{Bauer 11, example 1.7}). See at \emph{[[localization of a space]]} for more on this. \hypertarget{telescopic_localization}{}\subsubsection*{{Telescopic localization}}\label{telescopic_localization} \begin{itemize}% \item [[telescopic localization]] \end{itemize} \hypertarget{chromatic_localization}{}\subsubsection*{{Chromatic localization}}\label{chromatic_localization} \begin{itemize}% \item [[chromatic localization]] \end{itemize} \hypertarget{related_concepts}{}\subsection*{{Related concepts}}\label{related_concepts} \begin{itemize}% \item [[smashing localization]] \item [[chromatic filtration]], [[chromatic layer]] \item [[K(n)-local stable homotopy theory]] \end{itemize} \hypertarget{references}{}\subsection*{{References}}\label{references} Original articles are \begin{itemize}% \item [[Aldridge Bousfield]], \emph{The localization of spectra with respect to homology} , Topology vol 18 (1979) (\href{http://www.uio.no/studier/emner/matnat/math/MAT9580/v12/undervisningsmateriale/bousfield-topology-1979.pdf}{pdf}) \item [[Douglas Ravenel]], \emph{Localization with respect to certain periodic homology theories}, American Journal of Mathematics, Vol. 106, No. 2, (Apr., 1984), pp. 351-414 (\href{https://www.math.rochester.edu/people/faculty/doug/mypapers/loc.pdf}{pdf}) \end{itemize} Discussion in terms of [[Bousfield localization of model categories]] [[model category of spectra|of spectra]] appears in \begin{itemize}% \item [[Anthony Elmendorf]], [[Igor Kriz]], [[Michael Mandell]], [[Peter May]], chapter VIII of \emph{[[Rings, modules and algebras in stable homotopy theory]]} 1997 (\href{http://www.math.uchicago.edu/~may/BOOKS/EKMM.pdf}{pdf}) \item [[Stefan Schwede]], [[Brooke Shipley]], lemma 4.1 in \emph{A uniqueness theorem for stable homotopy theory}, Mathematische Zeitschrift 239 (2002), 803-828 (\href{https://arxiv.org/abs/math/0012021}{arXiv:math/0012021}) \end{itemize} see also \begin{itemize}% \item [[Carles Casacuberta]], [[Javier Gutiérrez]], \emph{Homotopical Localizations of Module Spectra}, Transactions of the American Mathematical Society Vol. 357, No. 7 (Jul., 2005), pp. 2753-2770 (\href{http://www.jstor.org/stable/3845180}{jstor}) \end{itemize} Lecture notes include \begin{itemize}% \item [[Nerses Aramian]], \emph{Bousfield Localization} (\href{http://www.math.uiuc.edu/~aramyan2/bousfield.pdf}{pdf}) \item [[Tilman Bauer]], \emph{Bousfield localization and the Hasse square}, 2011 (\href{http://math.mit.edu/conferences/talbot/2007/tmfproc/Chapter09/bauer.pdf}{pdf}) \item [[Paul VanKoughnett]], \emph{Spectra and localization}, 2013 ([[VanKoughnettLocalization.pdf:file]]) \end{itemize} Discussion the general context of [[higher algebra]]/[[stable homotopy theory]] includes \begin{itemize}% \item [[Jacob Lurie]], \emph{[[Chromatic Homotopy Theory]]}, Lecture notes (2010) (\href{http://www.math.harvard.edu/~lurie/252x.html}{web}), Lecture 20 \emph{Bousfield localization} (\href{http://www.math.harvard.edu/~lurie/252xnotes/Lecture20.pdf}{pdf}) \item [[Jacob Lurie]], section 4 of \emph{[[Proper Morphisms, Completions, and the Grothendieck Existence Theorem]]} \end{itemize} Discussion specifically of [[K(n)-local spectra]] includes \begin{itemize}% \item [[Michael Hopkins]], [[Jacob Lurie]], \emph{[[Ambidexterity in K(n)-Local Stable Homotopy Theory]]} \end{itemize} See also section 2.4 of \begin{itemize}% \item Holger Reeker, \emph{On K(1)-local SU-bordism} (\href{http://arxiv.org/abs/0907.4299}{arXiv:0907.4299}) \end{itemize} [[!redirects local spectrum]] [[!redirects local spectra]] [[!redirects localization of a spectrum]] [[!redirects localization of spectra]] [[!redirects localization of spectra]] [[!redirects localizations of spectra]] \end{document}