added remark that in the case of disjoint gluing the equalizer is also a fibered product
authorKevin Walker <kevin@canyon23.net>
Tue, 15 Mar 2011 17:11:47 -0700
changeset 724 3d751b59a7d8
parent 723 1b49432f3aef
child 725 e27bc92e5d9b
added remark that in the case of disjoint gluing the equalizer is also a fibered product
text/tqftreview.tex
--- a/text/tqftreview.tex	Tue Mar 15 16:49:49 2011 -0700
+++ b/text/tqftreview.tex	Tue Mar 15 17:11:47 2011 -0700
@@ -100,6 +100,8 @@
 maps, we get two maps $\cC_k(X) \to \cC(Y)$, corresponding to the two
 copies of $Y$ in $\bd X$.
 Let $\Eq_Y(\cC_k(X))$ denote the equalizer of these two maps.
+(When $X$ is a disjoint union $X_1\du X_2$ the equalizer is the same as the fibered product
+$\cC_k(X_1)\times_{\cC(Y)} \cC_k(X_2)$.)
 Then (here's the axiom/definition part) there is an injective ``gluing" map
 \[
 	\Eq_Y(\cC_k(X)) \hookrightarrow \cC_k(X\sgl) ,