diff -r 971234b03c4a -r 1c408505c9f5 text/ncat.tex --- a/text/ncat.tex Mon May 10 14:14:19 2010 -0700 +++ b/text/ncat.tex Mon May 10 19:34:59 2010 -0700 @@ -1127,7 +1127,7 @@ (The tensor product will depend (functorially) on the choice of $J$.) To a subdivision \[ - J = I_1\cup \cdots\cup I_m + J = I_1\cup \cdots\cup I_p \] we associate the chain complex \[ @@ -1184,13 +1184,68 @@ Now we reinterpret $(\cM_\cC\ot {_\cC\cN})^*$ as some sort of morphism $\cM_\cC \to (_\cC\cN)^*$. Let $f\in (\cM_\cC\ot {_\cC\cN})^*$. -Let $\olD$ be a chain of subdivisions with $D_0 = [J = I_1\cup\cdots\cup I_m]$, and let -$m\ot \cbar \in \cM(I_1)\ot\cC(I_2)\ot\cdots\ot\cC(I_{m-1})$. +Let $\olD = (D_0\cdots D_l)$ be a chain of subdivisions with $D_0 = [J = I_1\cup\cdots\cup I_m]$. +Recall that $(_\cC\cN)^*(I_1\cup\cdots\cup I_{p-1}) = (_\cC\cN(I_p))^*$. +Then for each such $\olD$ we have a degree $l$ map +\begin{eqnarray*} + \cM(I_1)\ot\cC(I_2)\ot\cdots\ot\cC(I_{p-1}) &\to& (_\cC\cN)^*(I_1\cup\cdots\cup I_{p-1}) \\ + m\ot \cbar &\mapsto& [n\mapsto f(\olD\ot m\ot \cbar\ot n)] +\end{eqnarray*} +We are almost ready to give the definition of morphisms between arbitrary modules +$\cX_\cC$ and $\cY_\cC$. +Note that the rightmost interval $I_m$ does not appear above, except implicitly in $\olD$. +To fix this, we define subdivisions are antirefinements of left-marked intervals. +Subdivisions are just the obvious thing, but antirefinements are defined to mimic +the above antirefinements of the fixed interval $J$, but with the rightmost subinterval $I_m$ always +omitted. +More specifically, $D\to D'$ is an antirefinement if $D'$ is obtained from $D$ by +gluing subintervals together and/or omitting some of the rightmost subintervals. +(See Figure xxxx.) + +Now we define the chain complex $\hom_\cC(\cX_\cC \to \cY_\cC)$. +The underlying vector space is +\[ + \prod_l \prod_{\olD} \hom[l]\left( + \cX(I_1)\ot\cC(I_2)\ot\cdots\ot\cC(I_{p-1}) \to + \cY(I_1\cup\cdots\cup I_{p-1}) \rule{0pt}{1.1em}\right) , +\] +where, as usual $\olD = (D_0\cdots D_l)$ is a chain of antirefinements +(but now of left-marked intervals) and $D_0$ is the subdivision $I_1\cup\cdots\cup I_{p-1}$. +$\hom[l](- \to -)$ means graded linear maps of degree $l$. - +\nn{small issue (pun intended): +the above is a vector space only if the class of subdivisions is a set, e.g. only if +all of our left-marked intervals are contained in some universal interval (like $J$ above). +perhaps we should give another version of the definition in terms of natural transformations of functors.} +Abusing notation slightly, we will denote elements of the above space by $g$, with +\[ + \olD\ot x \ot \cbar \mapsto g(\olD\ot x \ot \cbar) \in \cY(I_1\cup\cdots\cup I_{p-1}) . +\] +For fixed $D_0$ and $D_1$, let $\cbar = \cbar'\ot\cbar''$, where $\cbar'$ corresponds to the subintervals of $D_0$ which map to $D_1$ and $\cbar''$ corresponds to the subintervals +which are dropped off the right side. +(Either $\cbar'$ or $\cbar''$ might be empty.) +Translating from the boundary map for $(\cM_\cC\ot {_\cC\cN})^*$ \nn{give ref?}, +we have +\begin{eqnarray*} + (\bd g)(\olD\ot x \ot \cbar) &=& \bd(g(\olD\ot x \ot \cbar)) + g(\olD\ot\bd(x\ot\cbar)) + \\ + & & \;\; g((\bd_+\olD)\ot x\ot\cbar) + \gl(g((\bd_0\olD)\ot x\ot\cbar')\ot\cbar'') . +\end{eqnarray*} +Here $\gl$ denotes the module action in $\cY_\cC$. +This completes the definition of $\hom_\cC(\cX_\cC \to \cY_\cC)$. +Note that if $\bd g = 0$, then each +\[ + g(\olD\ot -) : \cX(I_1)\ot\cC(I_2)\ot\cdots\ot\cC(I_{p-1}) \to \cY(I_1\cup\cdots\cup I_{p-1}) +\] +constitutes a null homotopy of +$g((\bd \olD)\ot -)$ (where the $g((\bd_0 \olD)\ot -)$ part of $g((\bd \olD)\ot -)$ +should be interpreted as above). + +\nn{do we need to say anything about composing morphisms of modules?} + +\nn{should we define functors between $n$-cats in a similar way?} \nn{...}