diff -r 40df54ede7fe -r f0518720227a text/ncat.tex --- a/text/ncat.tex Tue Jun 22 18:56:51 2010 -0700 +++ b/text/ncat.tex Tue Jun 22 22:19:16 2010 -0700 @@ -1682,10 +1682,12 @@ whose objects are $n$-categories. When $n=2$ this is a version of the familiar algebras-bimodules-intertwiners $2$-category. -While it is clearly appropriate to call an $S^0$ module a bimodule, +It is clearly appropriate to call an $S^0$ module a bimodule, but this is much less true for higher dimensional spheres, so we prefer the term ``sphere module" for the general case. +For simplicity, we will assume that $n$-categories are enriched over $\c$-vector spaces. + The $0$- through $n$-dimensional parts of $\cC$ are various sorts of modules, and we describe these first. The $n{+}1$-dimensional part of $\cS$ consists of intertwiners @@ -1711,7 +1713,7 @@ Another way to say this is that $(X, M)$ is homeomorphic to $B^{k-1}\times([-1,1], \{0\})$. \begin{figure}[!ht] -$$\tikz[baseline,line width=2pt]{\draw[blue] (-2,0)--(2,0); \fill[red] (0,0) circle (0.1);} \qquad \qquad \tikz[baseline,line width=2pt]{\draw[blue] (0,0) circle (2 and 1); \draw[red] (0,1)--(0,-1);}$$ +$$\tikz[baseline,line width=2pt]{\draw[blue] (-2,0)--(2,0); \fill[red] (0,0) circle (0.1);} \qquad \qquad \tikz[baseline,line width=2pt]{\draw[blue][fill=blue!30!white] (0,0) circle (2 and 1); \draw[red] (0,1)--(0,-1);}$$ \caption{0-marked 1-ball and 0-marked 2-ball} \label{feb21a} \end{figure} @@ -1736,7 +1738,7 @@ or $\cB_k(X_i)$ (if $X_i$ lies on the $\cB$-labeled side) or $\cM_k(X_i)$ (if $X_i$ intersects the marking and is therefore a smaller 0-marked ball). Corresponding to this decomposition we have an action and/or composition map -from the product of these various sets into $\cM(X)$. +from the product of these various sets into $\cM_k(X)$. \medskip @@ -1761,7 +1763,7 @@ \draw (2,0) -- (4,0) node[below] {$J$}; \fill[red] (3,0) circle (0.1); -\draw (6,0) node(a) {} arc (135:90:4) node(top) {} arc (90:45:4) node(b) {} arc (-45:-90:4) node(bottom) {} arc(-90:-135:4); +\draw[fill=blue!30!white] (6,0) node(a) {} arc (135:90:4) node(top) {} arc (90:45:4) node(b) {} arc (-45:-90:4) node(bottom) {} arc(-90:-135:4); \draw[red] (top.center) -- (bottom.center); \fill (a) circle (0.1) node[left] {\color{green!50!brown} $a$}; \fill (b) circle (0.1) node[right] {\color{green!50!brown} $b$}; @@ -1836,7 +1838,7 @@ \begin{figure}[!ht] $$ \begin{tikzpicture}[baseline,line width = 2pt] -\draw[blue] (0,0) circle (2); +\draw[blue][fill=blue!15!white] (0,0) circle (2); \fill[red] (0,0) circle (0.1); \foreach \qm/\qa/\n in {70/-30/0, 120/95/1, -120/180/2} { \draw[red] (0,0) -- (\qm:2); @@ -1876,7 +1878,7 @@ \medskip -We can now define the $n$- or less dimensional part of our $n{+}1$-category $\cS$. +We can now define the $n$-or-less-dimensional part of our $n{+}1$-category $\cS$. Choose some collection of $n$-categories, then choose some collections of bimodules for these $n$-categories, then choose some collection of 1-sphere modules for the various possible marked 1-spheres labeled by the $n$-categories and bimodules, and so on. @@ -1897,7 +1899,7 @@ Thus the $k$-morphisms of $\cS$ (for $k\le n$) can be thought of as $n$-category $k{-}1$-sphere modules (generalizations of bimodules). -On the other hand, we can equally think of the $k$-morphisms as decorations on $k$-balls, +On the other hand, we can equally well think of the $k$-morphisms as decorations on $k$-balls, and from this (official) point of view it is clear that they satisfy all of the axioms of an $n{+}1$-category. (All of the axioms for the less-than-$n{+}1$-dimensional part of an $n{+}1$-category, that is.) @@ -1905,12 +1907,40 @@ \medskip Next we define the $n{+}1$-morphisms of $\cS$. +The construction of the 0- through $n$-morphisms was easy and tautological, but the +$n{+}1$-morphisms will require a bit of combinatorial topology effort, as well as addition +duality assumptions on the lower morphisms. - +Let $X$ be an $n{+}1$-ball, and let $c$ be a decoration of its boundary +by a cell complex labeled by 0- through $n$-morphisms, as above. +Choose an $n{-}1$-sphere $E\sub \bd X$ which divides +$\bd X$ into ``incoming" and ``outgoing" boundary $\bd_-X$ and $\bd_+X$. +Let $E_c$ denote $E$ decorated by the restriction of $c$ to $E$. +Recall from above the associated 1-category $\cS(E_c)$. +We can also have $\cS(E_c)$ modules $\cS(\bd_-X_c)$ and $\cS(\bd_+X_c)$. +Define +\[ + \cS(X; c; E) \deq \hom_{\cS(E_c)}(\cS(\bd_-X_c), \cS(\bd_+X_c)) . +\] - +We will show that if the sphere modules are equipped with a compatible family of +non-degenerate inner products, then there is a coherent family of isomorphisms +$\cS(X; c; E) \cong \cS(X; c; E')$ for all pairs of choices $E$ and $E'$. +This will allow us to define $\cS(X; e)$ independently of the choice of $E$. - +Let $Y$ be a decorated $n$-ball, and $\ol{Y}$ it's mirror image. +(We assume we are working in the unoriented category.) +Let $Y\cup\ol{Y}$ denote the decorated $n$-sphere obtained by gluing $Y$ and $\ol{Y}$ +along their common boundary. +An {\it inner product} on $\cS(Y)$ is a dual vector +\[ + z_Y : \cS(Y\cup\ol{Y}) \to \c. +\] +We will also use the notation +\[ + \langle a, b\rangle \deq z_Y(a\bullet \ol{b}) \in \c . +\] +An inner product is {\it non-degenerate} if \nn{...} @@ -1929,10 +1959,7 @@ Stuff that remains to be done (either below or in an appendix or in a separate section or in a separate paper): \begin{itemize} -\item spell out what difference (if any) Top vs PL vs Smooth makes \item discuss Morita equivalence -\item morphisms of modules; show that it's adjoint to tensor product -(need to define dual module for this) \item functors \end{itemize}