English

Extracting list colorings from large independent sets

Combinatorics 2015-12-29 v1

Abstract

We take an application of the Kernel Lemma by Kostochka and Yancey to its logical conclusion. The consequence is a sort of magical way to draw conclusions about list coloring (and online list coloring) just from the existence of an independent set incident to many edges. We use this to prove an Ore-degree version of Brooks' Theorem for online list-coloring. The Ore-degree of an edge xyxy in a graph GG is θ(xy)=dG(x)+dG(y)\theta(xy) = d_G(x) + d_G(y). The Ore-degree of GG is θ(G)=maxxyE(G)θ(xy)\theta(G) = \max_{xy\in E(G)}\theta(xy). We show that every graph with θ18\theta\ge18 and ωθ2\omega\le\frac{\theta}{2} is online θ2\left\lfloor \frac{\theta}{2}\right\rfloor -choosable. In addition, we prove an upper bound for online list-coloring triangle-free graphs: χOLΔ+114lg(Δ)\chi_{OL}\le\Delta+1-\lfloor\frac{1}{4}\lg(\Delta)\rfloor. Finally, we characterize Gallai trees as the connected graphs GG with no independent set incident to at least G|G| edges.

Keywords

Cite

@article{arxiv.1512.08130,
  title  = {Extracting list colorings from large independent sets},
  author = {Hal Kierstead and Landon Rabern},
  journal= {arXiv preprint arXiv:1512.08130},
  year   = {2015}
}

Comments

arXiv admin note: text overlap with arXiv:1406.7355