diff -r f5af4f863a8f -r a80cc9f9a65b text/ncat.tex --- a/text/ncat.tex Thu Apr 26 06:57:24 2012 -0600 +++ b/text/ncat.tex Fri Apr 27 22:37:14 2012 -0700 @@ -131,7 +131,7 @@ \begin{lem} \label{lem:spheres} -For each $1 \le k \le n$, we have a functor $\cl{\cC}_{k-1}$ from +For each $1 \le k \le n$, we have a functor $\colimit{\cC}_{k-1}$ from the category of $k{-}1$-spheres and homeomorphisms to the category of sets and bijections. \end{lem} @@ -146,13 +146,13 @@ \begin{axiom}[Boundaries]\label{nca-boundary} -For each $k$-ball $X$, we have a map of sets $\bd: \cC_k(X)\to \cl{\cC}_{k-1}(\bd X)$. +For each $k$-ball $X$, we have a map of sets $\bd: \cC_k(X)\to \colimit{\cC}_{k-1}(\bd X)$. These maps, for various $X$, comprise a natural transformation of functors. \end{axiom} Note that the first ``$\bd$" above is part of the data for the category, while the second is the ordinary boundary of manifolds. -Given $c\in\cl{\cC}(\bd(X))$, we will write $\cC(X; c)$ for $\bd^{-1}(c)$, those morphisms with specified boundary $c$. +Given $c\in\colimit{\cC}(\bd(X))$, we will write $\cC(X; c)$ for $\bd^{-1}(c)$, those morphisms with specified boundary $c$. \medskip @@ -176,21 +176,21 @@ domain and range, but the converse meets with our approval. That is, given compatible domain and range, we should be able to combine them into the full boundary of a morphism. -The following lemma will follow from the colimit construction used to define $\cl{\cC}_{k-1}$ +The following lemma will follow from the colimit construction used to define $\colimit{\cC}_{k-1}$ on spheres. \begin{lem}[Boundary from domain and range] \label{lem:domain-and-range} Let $S = B_1 \cup_E B_2$, where $S$ is a $k{-}1$-sphere $(1\le k\le n)$, $B_i$ is a $k{-}1$-ball, and $E = B_1\cap B_2$ is a $k{-}2$-sphere (Figure \ref{blah3}). -Let $\cC(B_1) \times_{\cl{\cC}(E)} \cC(B_2)$ denote the fibered product of the -two maps $\bd: \cC(B_i)\to \cl{\cC}(E)$. +Let $\cC(B_1) \times_{\colimit{\cC}(E)} \cC(B_2)$ denote the fibered product of the +two maps $\bd: \cC(B_i)\to \colimit{\cC}(E)$. Then we have an injective map \[ - \gl_E : \cC(B_1) \times_{\cl{\cC}(E)} \cC(B_2) \into \cl{\cC}(S) + \gl_E : \cC(B_1) \times_{\colimit{\cC}(E)} \cC(B_2) \into \colimit{\cC}(S) \] which is natural with respect to the actions of homeomorphisms. -(When $k=1$ we stipulate that $\cl{\cC}(E)$ is a point, so that the above fibered product +(When $k=1$ we stipulate that $\colimit{\cC}(E)$ is a point, so that the above fibered product becomes a normal product.) \end{lem} @@ -217,20 +217,20 @@ with respect to $E$. On the other hand, in categories based on maps to a target space (c.f. Example \ref{ex:maps-to-a-space} below) the gluing map is always surjective. If $S$ is a 0-sphere (the case $k=1$ above), then $S$ can be identified with the {\it disjoint} union -of two 0-balls $B_1$ and $B_2$ and the colimit construction $\cl{\cC}(S)$ can be identified +of two 0-balls $B_1$ and $B_2$ and the colimit construction $\colimit{\cC}(S)$ can be identified with the (ordinary, not fibered) product $\cC(B_1) \times \cC(B_2)$. -Let $\cl{\cC}(S)\trans E$ denote the image of $\gl_E$. -We will refer to elements of $\cl{\cC}(S)\trans E$ as ``splittable along $E$" or ``transverse to $E$". +Let $\colimit{\cC}(S)\trans E$ denote the image of $\gl_E$. +We will refer to elements of $\colimit{\cC}(S)\trans E$ as ``splittable along $E$" or ``transverse to $E$". When the gluing map is surjective every such element is splittable. If $X$ is a $k$-ball and $E \sub \bd X$ splits $\bd X$ into two $k{-}1$-balls $B_1$ and $B_2$ -as above, then we define $\cC(X)\trans E = \bd^{-1}(\cl{\cC}(\bd X)\trans E)$. - -We will call the projection $\cl{\cC}(S)\trans E \to \cC(B_i)$ given by the composition -$$\cl{\cC}(S)\trans E \xrightarrow{\gl^{-1}} \cC(B_1) \times \cC(B_2) \xrightarrow{\pr_i} \cC(B_i)$$ +as above, then we define $\cC(X)\trans E = \bd^{-1}(\colimit{\cC}(\bd X)\trans E)$. + +We will call the projection $\colimit{\cC}(S)\trans E \to \cC(B_i)$ given by the composition +$$\colimit{\cC}(S)\trans E \xrightarrow{\gl^{-1}} \cC(B_1) \times \cC(B_2) \xrightarrow{\pr_i} \cC(B_i)$$ a {\it restriction} map and write $\res_{B_i}(a)$ -(or simply $\res(a)$ when there is no ambiguity), for $a\in \cl{\cC}(S)\trans E$. +(or simply $\res(a)$ when there is no ambiguity), for $a\in \colimit{\cC}(S)\trans E$. More generally, we also include under the rubric ``restriction map" the boundary maps of Axiom \ref{nca-boundary} above, another class of maps introduced after Axiom \ref{nca-assoc} below, as well as any composition @@ -238,7 +238,7 @@ In particular, we have restriction maps $\cC(X)\trans E \to \cC(B_i)$ defined as the composition of the boundary with the first restriction map described above: $$ -\cC(X) \trans E \xrightarrow{\bdy} \cl{\cC}(\bdy X)\trans E \xrightarrow{\res} \cC(B_i) +\cC(X) \trans E \xrightarrow{\bdy} \colimit{\cC}(\bdy X)\trans E \xrightarrow{\res} \cC(B_i) .$$ These restriction maps can be thought of as domain and range maps, relative to the choice of splitting $\bd X = B_1 \cup_E B_2$. @@ -317,7 +317,7 @@ In situations where the splitting is notationally anonymous, we will write $\cC(X)\spl$ for the morphisms which are splittable along (a.k.a.\ transverse to) the unnamed splitting. -If $\beta$ is a ball decomposition of $\bd X$, we define $\cC(X)_\beta \deq \bd\inv(\cl{\cC}(\bd X)_\beta)$; +If $\beta$ is a ball decomposition of $\bd X$, we define $\cC(X)_\beta \deq \bd\inv(\colimit{\cC}(\bd X)_\beta)$; this can also be denoted $\cC(X)\spl$ if the context contains an anonymous decomposition of $\bd X$ and no competing splitting of $X$. @@ -995,7 +995,7 @@ Most of the examples of $n$-categories we are interested in are enriched in the following sense. The various sets of $n$-morphisms $\cC(X; c)$, for all $n$-balls $X$ and -all $c\in \cl{\cC}(\bd X)$, have the structure of an object in some appropriate auxiliary category +all $c\in \colimit{\cC}(\bd X)$, have the structure of an object in some appropriate auxiliary category (e.g.\ vector spaces, or modules over some ring, or chain complexes), and all the structure maps of the $n$-category are compatible with the auxiliary category structure. @@ -1021,7 +1021,7 @@ we need a preliminary definition. Once we have the above $n$-category axioms for $n{-}1$-morphisms, we can define the category $\bbc$ of {\it $n$-balls with boundary conditions}. -Its objects are pairs $(X, c)$, where $X$ is an $n$-ball and $c \in \cl\cC(\bd X)$ is the ``boundary condition". +Its objects are pairs $(X, c)$, where $X$ is an $n$-ball and $c \in \colimit{\cC}(\bd X)$ is the ``boundary condition". The morphisms from $(X, c)$ to $(X', c')$, denoted $\Homeo(X; c \to X'; c')$, are homeomorphisms $f:X\to X'$ such that $f|_{\bd X}(c) = c'$. %Let $\pi_0(\bbc)$ denote @@ -1038,7 +1038,7 @@ \item Composition. Let $B = B_1\cup_Y B_2$ as in Axiom \ref{axiom:composition}. Let $Y_i = \bd B_i \setmin Y$. Note that $\bd B = Y_1\cup Y_2$. -Let $c_i \in \cC(Y_i)$ with $\bd c_1 = \bd c_2 = d \in \cl\cC(E)$. +Let $c_i \in \cC(Y_i)$ with $\bd c_1 = \bd c_2 = d \in \colimit{\cC}(E)$. Then we have a map \[ \gl_Y : \bigoplus_c \cC(B_1; c_1 \bullet c) \otimes \cC(B_2; c_2\bullet c) \to \cC(B; c_1\bullet c_2), @@ -1073,7 +1073,7 @@ \begin{axiom}[\textup{\textbf{[$A_\infty$ replacement for Axiom \ref{axiom:extended-isotopies}]}} Families of homeomorphisms act in dimension $n$.] \label{axiom:families} -For each pair of $n$-balls $X$ and $X'$ and each pair $c\in \cl{\cC}(\bd X)$ and $c'\in \cl{\cC}(\bd X')$ we have an $\cS$-morphism +For each pair of $n$-balls $X$ and $X'$ and each pair $c\in \colimit{\cC}(\bd X)$ and $c'\in \colimit{\cC}(\bd X')$ we have an $\cS$-morphism \[ \cJ(\Homeo(X;c \to X'; c')) \ot \cC(X; c) \to \cC(X'; c') . \] @@ -1184,7 +1184,7 @@ An $n$-category consists of the following data: \begin{itemize} \item functors $\cC_k$ from $k$-balls to sets, $0\le k\le n$ (Axiom \ref{axiom:morphisms}); -\item boundary natural transformations $\cC_k \to \cl{\cC}_{k-1} \circ \bd$ (Axiom \ref{nca-boundary}); +\item boundary natural transformations $\cC_k \to \colimit{\cC}_{k-1} \circ \bd$ (Axiom \ref{nca-boundary}); \item ``composition'' or ``gluing'' maps $\gl_Y : \cC(B_1)\trans E \times_{\cC(Y)} \cC(B_2)\trans E \to \cC(B_1\cup_Y B_2)\trans E$ (Axiom \ref{axiom:composition}); \item ``product'' or ``identity'' maps $\pi^*:\cC(X)\to \cC(E)$ for each pinched product $\pi:E\to X$ (Axiom \ref{axiom:product}); \item if enriching in an auxiliary category, additional structure on $\cC_n(X; c)$ (Axiom \ref{axiom:enriched}); @@ -1268,7 +1268,7 @@ Let $W$ be an $n{-}j$-manifold. Define the $j$-category $\cF(W)$ as follows. If $X$ is a $k$-ball with $k