The four color proof suffices. An unavoidable set of configurations in planar triangulations. An attempt to understand the four color problem. Every planar map is four colorable. Every planar map is four colorable.
Every planar map is four colorable.
A proof of the four color theorem. Every planar map is four colorable. The existence of unavoidable sets of geographically good configurations. An existence theorem for planar maps. Every planar map is four colorable.