text/ncat.tex
changeset 795 4d66ffe8dc85
parent 789 787914e9e859
child 796 d30537de52c7
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   674 and all the structure maps of the $n$-category are compatible with the auxiliary
   674 and all the structure maps of the $n$-category are compatible with the auxiliary
   675 category structure.
   675 category structure.
   676 Note that this auxiliary structure is only in dimension $n$; if $\dim(Y) < n$ then 
   676 Note that this auxiliary structure is only in dimension $n$; if $\dim(Y) < n$ then 
   677 $\cC(Y; c)$ is just a plain set.
   677 $\cC(Y; c)$ is just a plain set.
   678 
   678 
   679 We will aim for a little bit more generality than we need and not assume that the objects
   679 %We will aim for a little bit more generality than we need and not assume that the objects
   680 of our auxiliary category are sets with extra structure.
   680 %of our auxiliary category are sets with extra structure.
   681 First we must specify requirements for the auxiliary category.
   681 First we must specify requirements for the auxiliary category.
   682 It should have a {\it distributive monoidal structure} in the sense of 
   682 It should have a {\it distributive monoidal structure} in the sense of 
   683 \nn{Stolz and Teichner, Traces in monoidal categories, 1010.4527}.
   683 \nn{Stolz and Teichner, Traces in monoidal categories, 1010.4527}.
   684 This means that there is a monoidal structure $\otimes$ and also coproduct $\oplus$,
   684 This means that there is a monoidal structure $\otimes$ and also coproduct $\oplus$,
   685 and these two structures interact in the appropriate way.
   685 and these two structures interact in the appropriate way.
   686 Examples include 
   686 Examples include 
   687 \begin{itemize}
   687 \begin{itemize}
   688 \item vector spaces (or $R$-modules or chain complexes) with tensor product and direct sum; and
   688 \item vector spaces (or $R$-modules or chain complexes) with tensor product and direct sum; and
   689 \item topological spaces with product and disjoint union.
   689 \item topological spaces with product and disjoint union.
   690 \end{itemize}
   690 \end{itemize}
       
   691 For convenience, we will also assume that the objects of our auxiliary category are sets with extra structure.
       
   692 (Otherwise, stating the axioms for identity morphisms becomes more cumbersome.)
       
   693 
   691 Before stating the revised axioms for an $n$-category enriched in a distributive monoidal category,
   694 Before stating the revised axioms for an $n$-category enriched in a distributive monoidal category,
   692 we need a preliminary definition.
   695 we need a preliminary definition.
   693 Once we have the above $n$-category axioms for $n{-}1$-morphisms, we can define the 
   696 Once we have the above $n$-category axioms for $n{-}1$-morphisms, we can define the 
   694 category $\bbc$ of {\it $n$-balls with boundary conditions}.
   697 category $\bbc$ of {\it $n$-balls with boundary conditions}.
   695 Its objects are pairs $(X, c)$, where $X$ is an $n$-ball and $c \in \cl\cC(\bd X)$ is the ``boundary condition".
   698 Its objects are pairs $(X, c)$, where $X$ is an $n$-ball and $c \in \cl\cC(\bd X)$ is the ``boundary condition".
   710 \[
   713 \[
   711 	\gl_Y : \bigoplus_c \cC(B_1; c_1 \bullet c) \otimes \cC(B_2; c_2\bullet c) \to \cC(B; c_1\bullet c_2),
   714 	\gl_Y : \bigoplus_c \cC(B_1; c_1 \bullet c) \otimes \cC(B_2; c_2\bullet c) \to \cC(B; c_1\bullet c_2),
   712 \]
   715 \]
   713 where the sum is over $c\in\cC(Y)$ such that $\bd c = d$.
   716 where the sum is over $c\in\cC(Y)$ such that $\bd c = d$.
   714 This map is natural with respect to the action of homeomorphisms and with respect to restrictions.
   717 This map is natural with respect to the action of homeomorphisms and with respect to restrictions.
   715 \item Product morphisms. \nn{Hmm... not sure what to say here. maybe we need sets with structure after all.}
   718 %\item Product morphisms. \nn{Hmm... not sure what to say here. maybe we need sets with structure after all.}
   716 \end{itemize}
   719 \end{itemize}
   717 \end{axiom}
   720 \end{axiom}
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