Three-edge-coloring projective planar cubic graphs: A generalization of the Four Color Theorem

Yuta Inoue, Ken-ichi Kawarabayashi, Atsuyuki Miyashita +2

We prove that every cyclically 4-edge-connected cubic graph that can be embedded in the projective plane, with the single exception of the Petersen graph, is 3-edge-colorable. In o…