Talk:Integral homology 3-spheres embed in the 4-sphere (Ex)
From Manifold Atlas
Let be a homology -sphere. By Freedman, there exists a (unique) contractible topological -manifold with .
Let , where we identify the two copies of in the boundary by the identity. Since , Seifert van Kampen says that . Moreover, And , so the Mayer-Vietoris sequence says that . In particular, , so by Freedman’s theorem is homeomorphic to . Therefore,Tex syntax erroris a (topological) embedding of into .