Coloring of Plane Graphs with Unique Maximal Colors on Faces

The Four Color Theorem asserts that the vertices of every plane graph can be properly colored with four colors. Fabrici and Goring conjectured the following stronger statement to also hold: the vertices of every plane graph can be properly colored with the numbers 1, …, 4 in such a way that every face contains a unique vertex colored with the maximal color appearing on that face. They proved that every plane graph has such a coloring with the numbers 1, …, 6. We prove that every plane graph has such a coloring with the numbers 1, …, 5 and we also prove the list variant of the statement for lists of sizes seven.