diff -r 77b0cdeb0fcd -r 217b6a870532 text/basic_properties.tex --- a/text/basic_properties.tex Thu Mar 18 19:40:46 2010 +0000 +++ b/text/basic_properties.tex Sat Mar 27 03:07:45 2010 +0000 @@ -3,10 +3,11 @@ \section{Basic properties of the blob complex} \label{sec:basic-properties} -\begin{prop} \label{disjunion} -There is a natural isomorphism $\bc_*(X \du Y) \cong \bc_*(X) \otimes \bc_*(Y)$. -\end{prop} -\begin{proof} +In this section we complete the proofs of Properties 1-4. Throughout the paper, where possible, we prove results using Properties 1-4, rather than the actual definition of blob homology. This allows the possibility of future improvements to or alternatives on our definition. In fact, we hope that there may be a characterisation of blob homology in terms of Properties 1-4, but at this point we are unaware of one. + +Recall Property \ref{property:disjoint-union}, that there is a natural isomorphism $\bc_*(X \du Y) \cong \bc_*(X) \otimes \bc_*(Y)$. + +\begin{proof}[Proof of Property \ref{property:disjoint-union}] Given blob diagrams $b_1$ on $X$ and $b_2$ on $Y$, we can combine them (putting the $b_1$ blobs before the $b_2$ blobs in the ordering) to get a blob diagram $(b_1, b_2)$ on $X \du Y$. @@ -14,10 +15,8 @@ In the other direction, any blob diagram on $X\du Y$ is equal (up to sign) to one that puts $X$ blobs before $Y$ blobs in the ordering, and so determines a pair of blob diagrams on $X$ and $Y$. -These two maps are compatible with our sign conventions. +These two maps are compatible with our sign conventions. (We follow the usual convention for tensors products of complexes, as in e.g. \cite{MR1438306}: $d(a \tensor b) = da \tensor b + (-1)^{\deg(a)} a \tensor db$.) The two maps are inverses of each other. -\nn{should probably say something about sign conventions for the differential -in a tensor product of chain complexes; ask Scott} \end{proof} For the next proposition we will temporarily restore $n$-manifold boundary @@ -44,8 +43,8 @@ Define $h_0 : \bc_0(B^n; c) \to \bc_1(B^n; c)$ by setting $h_0(x)$ equal to the 1-blob with blob $B^n$ and label $x - s(p(x)) \in U(B^n; c)$. \end{proof} - -Note that if there is no splitting $s$, we can let $h_0 = 0$ and get a homotopy +This proves Property \ref{property:contractibility} (the second half of the statement of this Property was immediate from the definitions). +Note that even when there is no splitting $s$, we can let $h_0 = 0$ and get a homotopy equivalence to the 2-step complex $U(B^n; c) \to \cC(B^n; c)$. For fields based on $n$-categories, $H_0(\bc_*(B^n; c)) \cong \mor(c', c'')$, @@ -56,7 +55,7 @@ \end{cor} \begin{proof} -This follows from \ref{disjunion} and \ref{bcontract}. +This follows from Properties \ref{property:disjoint-union} and \ref{property:contractibility}. \end{proof} Define the {\it support} of a blob diagram to be the union of all the @@ -84,37 +83,6 @@ so $f$ and the identity map are homotopic. \end{proof} - -\medskip - -\nn{Maybe there is no longer a need to repeat the next couple of props here, since we also state them in the introduction. -But I think it's worth saying that the Diff actions will be enhanced later. -Maybe put that in the intro too.} - -As we noted above, -\begin{prop} -There is a natural isomorphism $H_0(\bc_*(X)) \cong A(X)$. -\qed -\end{prop} - - -\begin{prop} -For fixed fields ($n$-cat), $\bc_*$ is a functor from the category -of $n$-manifolds and homeomorphisms to the category of chain complexes and -(chain map) isomorphisms. -\qed -\end{prop} - -In particular, -\begin{prop} \label{diff0prop} -There is an action of $\Homeo(X)$ on $\bc_*(X)$. -\qed -\end{prop} - -The above will be greatly strengthened in Section \ref{sec:evaluation}. - -\medskip - For the next proposition we will temporarily restore $n$-manifold boundary conditions to the notation. @@ -124,9 +92,9 @@ Given compatible fields (boundary conditions) $a$, $b$ and $c$ on $Y$, $-Y$ and $Z$, we have the blob complex $\bc_*(X; a, b, c)$. If $b = -a$ (the orientation reversal of $a$), then we can glue up blob diagrams on -$X$ to get blob diagrams on $X\sgl$: +$X$ to get blob diagrams on $X\sgl$. This proves Property \ref{property:gluing-map}, which we restate here in more detail. -\begin{prop} +\textbf{Property \ref{property:gluing-map}.}\emph{ There is a natural chain map \eq{ \gl: \bigoplus_a \bc_*(X; a, -a, c) \to \bc_*(X\sgl; c\sgl). @@ -134,22 +102,7 @@ The sum is over all fields $a$ on $Y$ compatible at their ($n{-}2$-dimensional) boundaries with $c$. `Natural' means natural with respect to the actions of diffeomorphisms. -\qed -\end{prop} - -The above map is very far from being an isomorphism, even on homology. -This will be fixed in Section \ref{sec:gluing} below. - -%\nn{Next para not needed, since we already use bullet = gluing notation above(?)} +} -%An instance of gluing we will encounter frequently below is where $X = X_1 \du X_2$ -%and $X\sgl = X_1 \cup_Y X_2$. -%(Typically one of $X_1$ or $X_2$ is a disjoint union of balls.) -%For $x_i \in \bc_*(X_i)$, we introduce the notation -%\eq{ -% x_1 \bullet x_2 \deq \gl(x_1 \otimes x_2) . -%} -%Note that we have resumed our habit of omitting boundary labels from the notation. - - - +This map is very far from being an isomorphism, even on homology. +We fix this deficit in Section \ref{sec:gluing} below.