diff -r 8d3f0bc6a76e -r a1136f6ff0f6 text/ncat.tex --- a/text/ncat.tex Tue Dec 22 21:18:07 2009 +0000 +++ b/text/ncat.tex Tue Jan 05 20:50:36 2010 +0000 @@ -23,6 +23,7 @@ \medskip Consider first ordinary $n$-categories. +\nn{Actually, we're doing both plain and infinity cases here} We need a set (or sets) of $k$-morphisms for each $0\le k \le n$. We must decide on the ``shape" of the $k$-morphisms. Some $n$-category definitions model $k$-morphisms on the standard bihedron (interval, bigon, ...). @@ -66,14 +67,15 @@ (Note: We usually omit the subscript $k$.) -We are so far being deliberately vague about what flavor of manifolds we are considering. +We are so far being deliberately vague about what flavor of $k$-balls +we are considering. They could be unoriented or oriented or Spin or $\mbox{Pin}_\pm$. They could be topological or PL or smooth. -\nn{need to check whether this makes much difference --- see pseudo-isotopy below} +%\nn{need to check whether this makes much difference} (If smooth, ``homeomorphism" should be read ``diffeomorphism", and we would need to be fussier about corners.) For each flavor of manifold there is a corresponding flavor of $n$-category. -We will concentrate of the case of PL unoriented manifolds. +We will concentrate on the case of PL unoriented manifolds. Next we consider domains and ranges of morphisms (or, as we prefer to say, boundaries of morphisms). @@ -95,7 +97,7 @@ (In order to conserve symbols, we use the same symbol $\cC_k$ for both morphisms and boundaries.) -\begin{axiom}[Boundaries (maps)] +\begin{axiom}[Boundaries (maps)]\label{nca-boundary} For each $k$-ball $X$, we have a map of sets $\bd: \cC(X)\to \cC(\bd X)$. These maps, for various $X$, comprise a natural transformation of functors. \end{axiom} @@ -161,21 +163,29 @@ \end{tikzpicture} $$ $$\mathfig{.4}{tempkw/blah3}$$ -\caption{Combining two balls to get a full boundary}\label{blah3}\end{figure} +\caption{Combining two balls to get a full boundary +\nn{maybe smaller dots for $E$ in pdf fig}}\label{blah3}\end{figure} Note that we insist on injectivity above. Let $\cC(S)_E$ denote the image of $\gl_E$. We will refer to elements of $\cC(S)_E$ as ``splittable along $E$" or ``transverse to $E$". +If $X$ is a $k$-ball and $E \sub \bd X$ splits $\bd X$ into two $k{-}1$-balls $B_1$ and $B_2$ +as above, then we define $\cC(X)_E = \bd^{-1}(\cC(\bd X)_E)$. + We will call the projection $\cC(S)_E \to \cC(B_i)$ a {\it restriction} map and write $\res_{B_i}(a)$ (or simply $\res(a)$ when there is no ambiguity), for $a\in \cC(S)_E$. -These restriction maps can be thought of as -domain and range maps, relative to the choice of splitting $S = B_1 \cup_E B_2$. +More generally, we also include under the rubric ``restriction map" the +the boundary maps of Axiom \ref{nca-boundary} above, +another calss of maps introduced after Axion \ref{nca-assoc} below, as well as any composition +of restriction maps (inductive definition). +In particular, we have restriction maps $\cC(X)_E \to \cC(B_i)$ +($i = 1, 2$, notation from previous paragraph). +These restriction maps can be thought of as +domain and range maps, relative to the choice of splitting $\bd X = B_1 \cup_E B_2$. -If $B$ is a $k$-ball and $E \sub \bd B$ splits $\bd B$ into two $k{-}1$-balls -as above, then we define $\cC(B)_E = \bd^{-1}(\cC(\bd B)_E)$. Next we consider composition of morphisms. For $n$-categories which lack strong duality, one usually considers @@ -205,7 +215,7 @@ $$\mathfig{.4}{tempkw/blah5}$$ \caption{From two balls to one ball}\label{blah5}\end{figure} -\begin{axiom}[Strict associativity] +\begin{axiom}[Strict associativity] \label{nca-assoc} The composition (gluing) maps above are strictly associative. \end{axiom} @@ -217,10 +227,10 @@ Notation: $a\bullet b \deq \gl_Y(a, b)$ and/or $a\cup b \deq \gl_Y(a, b)$. In the other direction, we will call the projection from $\cC(B)_E$ to $\cC(B_i)_E$ -a {\it restriction} map and write $\res_{B_i}(a)$ for $a\in \cC(B)_E$. -Compositions of boundary and restriction maps will also be called restriction maps. -For example, if $B$ is a $k$-ball and $Y\sub \bd B$ is a $k{-}1$-ball, there is a -restriction map from $\cC(B)_{\bd Y}$ to $\cC(Y)$. +a restriction map (one of many types of map so called) and write $\res_{B_i}(a)$ for $a\in \cC(B)_E$. +%Compositions of boundary and restriction maps will also be called restriction maps. +%For example, if $B$ is a $k$-ball and $Y\sub \bd B$ is a $k{-}1$-ball, there is a +%restriction map from $\cC(B)_{\bd Y}$ to $\cC(Y)$. We will write $\cC(B)_Y$ for the image of $\gl_Y$ in $\cC(B)$. We will call $\cC(B)_Y$ morphisms which are splittable along $Y$ or transverse to $Y$. @@ -461,7 +471,7 @@ \medskip -\subsection{Examples of $n$-categories} +\subsection{Examples of $n$-categories}\ \ \nn{these examples need to be fleshed out a bit more}