text/ncat.tex
changeset 803 a96ffd48ea3d
parent 802 e3ddb8605e32
child 804 c6ab12960403
equal deleted inserted replaced
802:e3ddb8605e32 803:a96ffd48ea3d
  2585 We define product $n{+}1$-morphisms to be identity maps of modules.
  2585 We define product $n{+}1$-morphisms to be identity maps of modules.
  2586 
  2586 
  2587 To define (binary) composition of $n{+}1$-morphisms, choose the obvious common equator
  2587 To define (binary) composition of $n{+}1$-morphisms, choose the obvious common equator
  2588 then compose the module maps.
  2588 then compose the module maps.
  2589 The proof that this composition rule is associative is similar to the proof of Lemma \ref{equator-lemma}.
  2589 The proof that this composition rule is associative is similar to the proof of Lemma \ref{equator-lemma}.
       
  2590 
       
  2591 \medskip
       
  2592 
       
  2593 We end this subsection with some remarks about Morita equivalence of disklike $n$-categories.
       
  2594 Recall that two 1-categories $C$ and $D$ are Morita equivalent if and only if they are equivalent
       
  2595 objects in the 2-category of (linear) 1-categories, bimodules, and intertwinors.
       
  2596 Similarly, we define two disklike $n$-categories to be Morita equivalent if they are equivalent objects in the
       
  2597 $n{+}1$-category of sphere modules.
       
  2598 
       
  2599 Because of the strong duality enjoyed by disklike $n$-categories, the data for such an equivalence lives only in 
       
  2600 dimensions 1 and $n+1$ (the middle dimensions come along for free), and this data must satisfy
       
  2601 identities corresponding to Morse cancellations in $n{+}1$-manifolds.
       
  2602 \noop{ % the following doesn't work; need 2^(k+1) different N's, not 2*(k+1)
       
  2603 More specifically, the 1-dimensional part of the data is a 0-sphere module $M = {}_CM_D$ 
       
  2604 (categorified bimodule) connecting $C$ and $D$.
       
  2605 From $M$ we can construct various $k$-sphere modules $N^k_{j,E}$ for $0 \le k \le n$, $0\le j \le k$, and $E = C$ or $D$.
       
  2606 $N^k_{j,E}$ can be thought of as the graph of an index $j$ Morse function on the $k$-ball $B^k$
       
  2607 (so the graph lives in $B^k\times I = B^{k+1}$).
       
  2608 The positive side of the graph is labeled by $E$, the negative side by $E'$
       
  2609 (where $C' = D$ and $D' = C$), and the codimension-1 
       
  2610 submanifold separating the positive and negative regions is labeled by $M$.
       
  2611 We think of $N^k_{j,E}$ as a $k{+}1$-morphism connecting 
       
  2612 }
       
  2613 We plan on treating this in more detail in a future paper.
       
  2614 \nn{should add a few more details}
       
  2615