Cobordism Morse function
= Cobordism Morse function
{title2=$f:W\to[0,1]$}
The incoming and outgoing boundaries are the regular levels zero and one, and all <critical points> lie in the interior. Near the boundary use a collar coordinate as the function. The <Morse handle-attachment theorem> produces a relative chain group freely generated by the interior <critical points>. Thus $\chi(W,M_0)$ is the alternating sum of their <Morse indices>, regardless of how their <critical values> are ordered.