Representing 3-manifolds by Dehn spheres

Abstract

Let M be a closed orientable 3-manifold. A Dehn sphere S is a 2-sphere immersed in M with only double curve and triple point singularities. S fills M if S defines a cell decomposition of M. It is proven that every closed orientable 3-manifold has a filling Dehn sphere. Examples are given, and Johansson diagrams are proposed as a method for representing all closed orientable 3-manifolds.