527 Note that $X_1$ and $X_2$ can be identified with subsets of $X$, 

   527 Note that $X_1$ and $X_2$ can be identified with subsets of $X$, 

   528 but $X_1 \cap X_2$ might not be codimension 1, and indeed we might have $X_1 = X_2 = X$.

   528 but $X_1 \cap X_2$ might not be codimension 1, and indeed we might have $X_1 = X_2 = X$.

   529 We assume that there is a decomposition of $X$ into balls which is compatible with

   529 We assume that there is a decomposition of $X$ into balls which is compatible with

   530 $X_1$ and $X_2$.

   530 $X_1$ and $X_2$.

   531 Let $a\in \cC(X)$, and let $a_i$ denote the restriction of $a$ to $X_i\sub X$.

   531 Let $a\in \cC(X)$, and let $a_i$ denote the restriction of $a$ to $X_i\sub X$.

   532 Then 

   533 Then 

   533 \[

   534 \[

   534 	\pi^*(a) = \pi_1^*(a_1)\bullet \pi_2^*(a_2) .

   535 	\pi^*(a) = \pi_1^*(a_1)\bullet \pi_2^*(a_2) .

   535 \]

   536 \]

   536 \item

   537 \item