Definition:Cobordism/Homotopy

Definitions
Let $X^n$ and $Y^n$ be manifolds without boundary of dimension $n$.

Let $W$ be a cobordism between $X$ and $Y$ such that $W$ is homotopy-equivalent to $X \times \closedint 0 1$.

(formally, $\exists \phi: W \to X$ such that $\phi$ is a retract, which for $X$ and $Y$ simply connected is equivalent to $H_* \struct {W, M; \Z} = 0$)

Then $W$ is said to be an $h$-cobordism.