Embeddings of homology equivalent manifolds with boundary

Abstract

AbstractWe prove a theorem on equivariant maps implying the following two corollaries:(1) Let N and M be compact orientable n-manifolds with boundaries such that M⊂N, the inclusion M→N induces an isomorphism in integral cohomology, both M and N have (n−d−1)-dimensional spines and m⩾max{n+3,3n+2−d2}. Then the restriction-induced map Embm(N)→Embm(M) is bijective. Here Embm(X) is the set of embeddings X→Rm up to isotopy (in the PL or smooth category).(2) For a 3-manifold N with boundary whose integral homology groups are trivial and such that N≇D3 (or for its special 2-spine N) there exists an equivariant map N˜→S2, although N does not embed into R3.The second corollary completes the answer to the following question: for which pairs (m,n) for each n-polyhedron N the existence of an equivariant map N˜→Sm−1 implies embeddability of N into Rm? An answer was known for each pair (m,n) except (3,3) and (3,2)