Disjoint list-colorings for planar graphs
Abstract
One of Thomassen's classical results is that every planar graph of girth at least is 3-choosable. One can wonder if for a planar graph of girth sufficiently large and a -list-assignment , one can do even better. Can one find disjoint -colorings (a packing), or disjoint -colorings, or a collection of -colorings that to every vertex assigns every color on average in one third of the cases (a fractional packing)? We prove that the packing is impossible, but two disjoint -colorings are guaranteed if the girth is at least , and a fractional packing exists when the girth is at least For a graph , the least such that there are always disjoint proper list-colorings whenever we have lists all of size associated to the vertices is called the list packing number of . We lower the two-times-degeneracy upper bound for the list packing number of planar graphs of girth or . As immediate corollaries, we improve bounds for -flexibility of classes of planar graphs with a given girth. For instance, where previously Dvo\v{r}\'{a}k et al. proved that planar graphs of girth are (weighted) -flexibly -choosable for an extremely small value of , we obtain the optimal value . Finally, we completely determine and show interesting behavior on the packing numbers for -minor-free graphs for some small graphs
Cite
@article{arxiv.2312.17233,
title = {Disjoint list-colorings for planar graphs},
author = {Stijn Cambie and Wouter Cames van Batenburg and Xuding Zhu},
journal= {arXiv preprint arXiv:2312.17233},
year = {2023}
}
Comments
36 pages, 8 figures