On Choosability with Separation of Planar Graphs with Forbidden Cycles

We study choosability with separation which is a constrained version of list coloring of graphs. A (k, d)-list assignment L of 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- 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. (C) 2015 Wiley Periodicals, Inc.