diff -r 4e3a152f4936 -r 8efbd2730ef9 text/intro.tex --- a/text/intro.tex Fri Jan 07 14:19:50 2011 -0800 +++ b/text/intro.tex Fri Jan 07 14:40:58 2011 -0800 @@ -63,29 +63,30 @@ Thus, in the second part of the paper (\S\S \ref{sec:ncats}-\ref{sec:ainfblob}) we give yet another definition of an $n$-category, or rather a definition of an $n$-category with strong duality. (Removing the duality conditions from our definition would make it more complicated rather than less.) -We call these ``topological $n$-categories'', to differentiate them from previous versions. +We call these ``disk-like $n$-categories'', to differentiate them from previous versions. Moreover, we find that we need analogous $A_\infty$ $n$-categories, and we define these as well following very similar axioms. +(See \S \ref{n-cat-names} below for a discussion of $n$-category terminology.) The basic idea is that each potential definition of an $n$-category makes a choice about the ``shape" of morphisms. -We try to be as lax as possible: a topological $n$-category associates a vector space to every $B$ homeomorphic to the $n$-ball. +We try to be as lax as possible: a disk-like $n$-category associates a vector space to every $B$ homeomorphic to the $n$-ball. These vector spaces glue together associatively, and we require that there is an action of the homeomorphism groupoid. For an $A_\infty$ $n$-category, we associate a chain complex instead of a vector space to each such $B$ and ask that the action of homeomorphisms extends to a suitably defined action of the complex of singular chains of homeomorphisms. The axioms for an $A_\infty$ $n$-category are designed to capture two main examples: the blob complexes of $n$-balls labelled by a -topological $n$-category, and the complex $\CM{-}{T}$ of maps to a fixed target space $T$. +disk-like $n$-category, and the complex $\CM{-}{T}$ of maps to a fixed target space $T$. In \S \ref{ssec:spherecat} we explain how $n$-categories can be viewed as objects in an $n{+}1$-category of sphere modules. When $n=1$ this just the familiar 2-category of 1-categories, bimodules and intertwinors. -In \S \ref{ss:ncat_fields} we explain how to construct a system of fields from a topological $n$-category +In \S \ref{ss:ncat_fields} we explain how to construct a system of fields from a disk-like $n$-category (using a colimit along certain decompositions of a manifold into balls). With this in hand, we write $\bc_*(M; \cC)$ to indicate the blob complex of a manifold $M$ with the system of fields constructed from the $n$-category $\cC$. %\nn{KW: I don't think we use this notational convention any more, right?} In \S \ref{sec:ainfblob} we give an alternative definition of the blob complex for an $A_\infty$ $n$-category on an $n$-manifold (analogously, using a homotopy colimit). -Using these definitions, we show how to use the blob complex to ``resolve" any topological $n$-category as an +Using these definitions, we show how to use the blob complex to ``resolve" any ordinary $n$-category as an $A_\infty$ $n$-category, and relate the first and second definitions of the blob complex. We use the blob complex for $A_\infty$ $n$-categories to establish important properties of the blob complex (in both variants), in particular the ``gluing formula" of Theorem \ref{thm:gluing} below. @@ -105,7 +106,7 @@ \newcommand{\yyc}{6} \node[box] at (-4,\yyb) (tC) {$C$ \\ a `traditional' \\ weak $n$-category}; -\node[box] at (\xxa,\yya) (C) {$\cC$ \\ a topological \\ $n$-category}; +\node[box] at (\xxa,\yya) (C) {$\cC$ \\ a disk-like \\ $n$-category}; \node[box] at (\xxb,\yya) (A) {$\underrightarrow{\cC}(M)$ \\ the (dual) TQFT \\ Hilbert space}; \node[box] at (\xxa,\yyb) (FU) {$(\cF, U)$ \\ fields and\\ local relations}; \node[box] at (\xxb,\yyb) (BC) {$\bc_*(M; \cF)$ \\ the blob complex}; @@ -148,7 +149,7 @@ make connections between our definitions of $n$-categories and familiar definitions for $n=1$ and $n=2$, as well as relating the $n=1$ case of our $A_\infty$ $n$-categories with usual $A_\infty$ algebras. %Appendix \ref{sec:comm_alg} describes the blob complex when $\cC$ is a commutative algebra, -%thought of as a topological $n$-category, in terms of the topology of $M$. +%thought of as a disk-like $n$-category, in terms of the topology of $M$. %%%% this is said later in the intro %Throughout the paper we typically prefer concrete categories (vector spaces, chain complexes) @@ -371,15 +372,15 @@ for any homeomorphic pair $X$ and $Y$, satisfying corresponding conditions. -In \S \ref{sec:ncats} we introduce the notion of topological $n$-categories, from which we can construct systems of fields. -Below, when we talk about the blob complex for a topological $n$-category, we are implicitly passing first to this associated system of fields. -Further, in \S \ref{sec:ncats} we also have the notion of an $A_\infty$ $n$-category. In that section we describe how to use the blob complex to construct $A_\infty$ $n$-categories from topological $n$-categories: +In \S \ref{sec:ncats} we introduce the notion of disk-like $n$-categories, from which we can construct systems of fields. +Below, when we talk about the blob complex for a disk-like $n$-category, we are implicitly passing first to this associated system of fields. +Further, in \S \ref{sec:ncats} we also have the notion of an $A_\infty$ $n$-category. In that section we describe how to use the blob complex to construct $A_\infty$ $n$-categories from ordinary $n$-categories: \newtheorem*{ex:blob-complexes-of-balls}{Example \ref{ex:blob-complexes-of-balls}} \begin{ex:blob-complexes-of-balls}[Blob complexes of products with balls form an $A_\infty$ $n$-category] %\label{thm:blobs-ainfty} -Let $\cC$ be a topological $n$-category. +Let $\cC$ be an ordinary $n$-category. Let $Y$ be an $n{-}k$-manifold. There is an $A_\infty$ $k$-category $\bc_*(Y;\cC)$, defined on each $m$-ball $D$, for $0 \leq m < k$, to be the set $$\bc_*(Y;\cC)(D) = \cC(Y \times D)$$ and on $k$-balls $D$ to be the set @@ -389,12 +390,12 @@ Property \ref{property:gluing-map} and with the action of families of homeomorphisms given in Theorem \ref{thm:evaluation}. \end{ex:blob-complexes-of-balls} \begin{rem} -Perhaps the most interesting case is when $Y$ is just a point; then we have a way of building an $A_\infty$ $n$-category from a topological $n$-category. +Perhaps the most interesting case is when $Y$ is just a point; then we have a way of building an $A_\infty$ $n$-category from an ordinary $n$-category. We think of this $A_\infty$ $n$-category as a free resolution. \end{rem} There is a version of the blob complex for $\cC$ an $A_\infty$ $n$-category -instead of a topological $n$-category; this is described in \S \ref{sec:ainfblob}. +instead of an ordinary $n$-category; this is described in \S \ref{sec:ainfblob}. The definition is in fact simpler, almost tautological, and we use a different notation, $\cl{\cC}(M)$. The next theorem describes the blob complex for product manifolds, in terms of the $A_\infty$ blob complex of the $A_\infty$ $n$-categories constructed as in the previous example. %The notation is intended to reflect the close parallel with the definition of the TQFT skein module via a colimit. @@ -412,9 +413,9 @@ The statement can be generalized to arbitrary fibre bundles, and indeed to arbitrary maps (see \S \ref{ss:product-formula}). -Fix a topological $n$-category $\cC$, which we'll omit from the notation. +Fix a disk-like $n$-category $\cC$, which we'll omit from the notation. Recall that for any $(n-1)$-manifold $Y$, the blob complex $\bc_*(Y)$ is naturally an $A_\infty$ category. -(See Appendix \ref{sec:comparing-A-infty} for the translation between topological $A_\infty$ $1$-categories and the usual algebraic notion of an $A_\infty$ category.) +(See Appendix \ref{sec:comparing-A-infty} for the translation between disk-like $A_\infty$ $1$-categories and the usual algebraic notion of an $A_\infty$ category.) \newtheorem*{thm:gluing}{Theorem \ref{thm:gluing}}