diff -r 56a31852242e -r bb7e388b9704 text/appendixes/comparing_defs.tex --- a/text/appendixes/comparing_defs.tex Sun Jul 18 18:26:05 2010 -0600 +++ b/text/appendixes/comparing_defs.tex Mon Jul 19 07:45:26 2010 -0600 @@ -3,11 +3,25 @@ \section{Comparing $n$-category definitions} \label{sec:comparing-defs} -In this appendix we relate the ``topological" category definitions of \S\ref{sec:ncats} -to more traditional definitions, for $n=1$ and 2. +In \S\ref{sec:example:traditional-n-categories(fields)} we showed how to construct +a topological $n$-category from a traditional $n$-category; the morphisms of the +topological $n$-category are string diagrams labeled by the traditional $n$-category. +In this appendix we sketch how to go the other direction, for $n=1$ and 2. +The basic recipe, given a topological $n$-category $\cC$, is to define the $k$-morphisms +of the corresponding traditional $n$-category to be $\cC(B^k)$, where +$B^k$ is the {\it standard} $k$-ball. +One must then show that the axioms of \S\ref{ss:n-cat-def} imply the traditional $n$-category axioms. +One should also show that composing the two arrows (between traditional and topological $n$-categories) +yields the appropriate sort of equivalence on each side. +Since we haven't given a definition for functors between topological $n$-categories +(the paper is already too long!), we do not pursue this here. +\nn{say something about modules and tensor products?} -\nn{cases to cover: (a) plain $n$-cats for $n=1,2$; (b) $n$-cat modules for $n=1$, also 2?; -(c) $A_\infty$ 1-cat; (b) $A_\infty$ 1-cat module?; (e) tensor products?} +We emphasize that we are just sketching some of the main ideas in this appendix --- +it falls well short of proving the definitions are equivalent. + +%\nn{cases to cover: (a) plain $n$-cats for $n=1,2$; (b) $n$-cat modules for $n=1$, also 2?; +%(c) $A_\infty$ 1-cat; (b) $A_\infty$ 1-cat module?; (e) tensor products?} \subsection{$1$-categories over $\Set$ or $\Vect$} \label{ssec:1-cats} @@ -34,8 +48,7 @@ If the underlying manifolds for $\cX$ have further geometric structure, then we obtain certain functors. The base case is for oriented manifolds, where we obtain no extra algebraic data. -For 1-categories based on unoriented manifolds (somewhat confusingly, we're thinking of being -unoriented as requiring extra data beyond being oriented, namely the identification between the orientations), +For 1-categories based on unoriented manifolds, there is a map $*:c(\cX)^1\to c(\cX)^1$ coming from $\cX$ applied to an orientation-reversing homeomorphism (unique up to isotopy) from $B^1$ to itself. @@ -52,8 +65,9 @@ For 1-categories based on $\text{Pin}_+$ manifolds, we have an order 2 antiautomorphism and also an order 2 automorphism of $c(\cX)^1$, and these two maps commute with each other. -\nn{need to also consider automorphisms of $B^0$ / objects} +%\nn{need to also consider automorphisms of $B^0$ / objects} +\noop{ \medskip In the other direction, given a $1$-category $C$ @@ -83,12 +97,14 @@ more or less exactly the same thing we started with. As we will see below, for $n>1$ the compositions yield a weaker sort of equivalence. +} %end \noop \medskip Similar arguments show that modules for topological 1-categories are essentially the same thing as traditional modules for traditional 1-categories. + \subsection{Plain 2-categories} \label{ssec:2-cats} Let $\cC$ be a topological 2-category.