Chromatic Homotopy Theory
《Chromatic Homotopy Theory》 · 第 345–346 页 · Section 11.1.1，Proposition 11.1.1 及其后定义
Every closed orientable 3-manifold \(M\) decomposes into two handlebodies of some genus \(g\). […] A decomposition of \(M\) into two handlebodies is called a Heegaard splitting. The two handlebodies have necessarily the same genus \(g\), since their boundaries are glued together and are hence diffeomorphic surfaces.