English

On hitting all maximum cliques with an independent set

Combinatorics 2010-03-16 v3

Abstract

We prove that every graph GG for which ω(G)3/4(Δ(G)+1)\omega(G) \geq 3/4(\Delta(G) + 1), has an independent set II such that ω(GI)<ω(G)\omega(G - I) < \omega(G). It follows that a minimum counterexample GG to Reed's conjecture satisfies ω(G)<3/4(Δ(G)+1)\omega(G) < 3/4(\Delta(G) + 1) and hence also χ(G)>7/6ω(G)\chi(G) > \lceil 7/6\omega(G) \rceil. We also prove that if for every induced subgraph HH of GG we have χ(H)max7/6ω(H),ω(H)+Δ(H)+12\chi(H) \leq \max{\lceil 7/6\omega(H) \rceil, \lceil \frac{\omega(H) + \Delta(H) + 1}{2}\rceil}, then we also have χ(G)ω(G)+Δ(G)+12\chi(G) \leq \lceil \frac{\omega(G) + \Delta(G) + 1}{2}\rceil. This gives a generic proof of the upper bound for line graphs of multigraphs proved by King et al.

Keywords

Cite

@article{arxiv.0907.3705,
  title  = {On hitting all maximum cliques with an independent set},
  author = {Landon Rabern},
  journal= {arXiv preprint arXiv:0907.3705},
  year   = {2010}
}

Comments

Added simple proof of Kostochka's lemma.