diff -r d8151afc725e -r c861ec0b1554 text/intro.tex --- a/text/intro.tex Fri May 06 18:02:06 2011 -0700 +++ b/text/intro.tex Sat May 07 08:35:36 2011 -0700 @@ -68,11 +68,14 @@ (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 disk-like $n$-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 +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 +The axioms for an $A_\infty$ $n$-category are designed to capture two main examples: +the blob complexes of $n$-balls labelled by a 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 @@ -151,14 +154,6 @@ %Appendix \ref{sec:comm_alg} describes the blob complex when $\cC$ is a commutative algebra, %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) -%even when we could work in greater generality (symmetric monoidal categories, model categories, etc.). - -%\item ? one of the points we make (far) below is that there is not really much -%difference between (a) systems of fields and local relations and (b) $n$-cats; -%thus we tend to switch between talking in terms of one or the other - \subsection{Motivations} @@ -259,10 +254,6 @@ Note that this includes the case of gluing two disjoint manifolds together. \begin{property}[Gluing map] \label{property:gluing-map}% -%If $X_1$ and $X_2$ are $n$-manifolds, with $Y$ a codimension $0$-submanifold of $\bdy X_1$, and $Y^{\text{op}}$ a codimension $0$-submanifold of $\bdy X_2$, there is a chain map -%\begin{equation*} -%\gl_Y: \bc_*(X_1) \tensor \bc_*(X_2) \to \bc_*(X_1 \cup_Y X_2). -%\end{equation*} Given a gluing $X \to X_\mathrm{gl}$, there is a natural map \[ @@ -372,9 +363,13 @@ for any homeomorphic pair $X$ and $Y$, satisfying corresponding conditions. -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: +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}} @@ -390,13 +385,16 @@ 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 an ordinary $n$-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 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 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. \newtheorem*{thm:product}{Theorem \ref{thm:product}} @@ -404,7 +402,8 @@ \begin{thm:product}[Product formula] Let $W$ be a $k$-manifold and $Y$ be an $n-k$ manifold. Let $\cC$ be an $n$-category. -Let $\bc_*(Y;\cC)$ be the $A_\infty$ $k$-category associated to $Y$ via blob homology (see Example \ref{ex:blob-complexes-of-balls}). +Let $\bc_*(Y;\cC)$ be the $A_\infty$ $k$-category associated to $Y$ via blob homology +(see Example \ref{ex:blob-complexes-of-balls}). Then \[ \bc_*(Y\times W; \cC) \simeq \cl{\bc_*(Y;\cC)}(W). @@ -532,7 +531,9 @@ by ``disk-like". (But beware: disks can come in various flavors, and some of them, such as framed disks, don't actually imply much duality.) -Another possibility considered here was ``pivotal $n$-category", but we prefer to preserve pivotal for its usual sense. It will thus be a theorem that our disk-like 2-categories are equivalent to pivotal 2-categories, c.f. \S \ref{ssec:2-cats}. +Another possibility considered here was ``pivotal $n$-category", but we prefer to preserve pivotal for its usual sense. +It will thus be a theorem that our disk-like 2-categories +are equivalent to pivotal 2-categories, c.f. \S \ref{ssec:2-cats}. Finally, we need a general name for isomorphisms between balls, where the balls could be piecewise linear or smooth or topological or Spin or framed or etc., or some combination thereof. @@ -566,7 +567,8 @@ Ansgar Schneider, and Dan Berwick-Evans. -\nn{need to double-check this list once the reading course is over} -During this work, Kevin Walker has been at Microsoft Station Q, and Scott Morrison has been at Microsoft Station Q and the Miller Institute for Basic Research at UC Berkeley. We'd like to thank the Aspen Center for Physics for the pleasant and productive +During this work, Kevin Walker has been at Microsoft Station Q, and Scott Morrison has been at +Microsoft Station Q and the Miller Institute for Basic Research at UC Berkeley. +We'd like to thank the Aspen Center for Physics for the pleasant and productive environment provided there during the final preparation of this manuscript.