H-cobordism theorem
= H-cobordism theorem
A compact smooth <h-cobordism> of dimension at least six between connected simply connected closed <manifolds> is <diffeomorphic> to a product, relative to its incoming boundary. The boundary <manifolds> consequently are <diffeomorphic>. The dimension and simple-connectivity hypotheses are sufficient conditions, not necessary properties of a product cylinder. The two boundary inclusions being <homotopy equivalences> are necessary for a <trivial cobordism>.