摘要
Let M be an orientable 3-manifold M whose boundary is a torus, and which does not contain an essential 2-sphere. The goal is to minimize the number of slopes on the boundary of M which produce essential 2-spheres by Dehn filling, via their minimal geometric intersection number. Earlier papers in this direction are [Topology 35 (2) (1996) 395–409] and [Topology Appl. 43 (1992) 213–218]. In 1996, Gordon and Luecke proved in [Topology 35 (2) (1996) 395–409] that the slopes on the boundary of M intersect exactly once. They proved this using the representations of types which come from the intersection of planar graphs.