is not greater than k − 1. The graph H∗
is simple because H is 3-connected. By Vizing’s theorem, H∗ admits a proper
edge-coloring with at most k colors. This coloring of H∗ induces a coloring of
H and also of G. On the small faces of G all edges have different colors, since
each such face correspond to a small faces of H.
induces
greater