On Choosability with Separation of Planar Graphs with Forbidden Cycles

TL;DR

This paper investigates a constrained list coloring problem called choosability with separation in planar graphs, proving new results about (3,1)-choosability for graphs without certain cycles.

Contribution

It establishes that planar graphs without 4, 5, or 6 cycles are (3,1)-choosable, and provides a new proof for triangle-free planar graphs' (3,1)-choosability.

Findings

Planar graphs without 4-cycles are (3,1)-choosable

Planar graphs without 5- or 6-cycles are (3,1)-choosable

Triangle-free planar graphs are (3,1)-choosable with a new proof

Abstract

We study choosability with separation which is a constrained version of list coloring of graphs. A (k,d)-list assignment L on a graph G is a function that assigns to each vertex v a list L(v) of at least k colors and for any adjacent pair xy, the lists L(x) and L(y) share at most d colors. A graph G is (k,d)-choosable if there exists an L-coloring of G for every (k,d)-list assignment L. This concept is also known as choosability with separation. We prove that planar graphs without 4-cycles are (3,1)-choosable and that planar graphs without 5-cycles and 6-cycles are (3,1)-choosable. In addition, we give an alternative and slightly stronger proof that triangle-free planar graphs are $(3,1)$-choosable.