Facial colorings using Hall's Theorem

Description

A vertex coloring of a plane graph is ℓ-facial if every two distinct vertices joined by a facial walk of length at most ℓ receive distinct colors. It has been conjectured that every plane graph has an ℓ-facial coloring with at most 3ℓ+1 colors. We improve the currently best known bound and show that every plane graph has an ℓ-facial coloring with at most 7ℓ/2+6 colors. Our proof uses the standard discharging technique, however, in the reduction part we have successfully applied Hall's Theorem, which seems to be quite an unusual approach in this area.

Abstract

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