
arXiv: 0907.3705
We prove that every graph $G$ for which $ω(G) \geq 3/4(Δ(G) + 1)$, has an independent set $I$ such that $ω(G - I) < ω(G)$. It follows that a minimum counterexample $G$ to Reed's conjecture satisfies $ω(G) < 3/4(Δ(G) + 1)$ and hence also $χ(G) > \lceil 7/6ω(G) \rceil$. We also prove that if for every induced subgraph $H$ of $G$ we have $χ(H) \leq \max{\lceil 7/6ω(H) \rceil, \lceil \frac{ω(H) + Δ(H) + 1}{2}\rceil}$, then we also have $χ(G) \leq \lceil \frac{ω(G) + Δ(G) + 1}{2}\rceil$. This gives a generic proof of the upper bound for line graphs of multigraphs proved by King et al.
Added simple proof of Kostochka's lemma.
clique, line graph, Extremal problems in graph theory, Vertex subsets with special properties (dominating sets, independent sets, cliques, etc.), FOS: Mathematics, Mathematics - Combinatorics, Combinatorics (math.CO), Reed's conjecture, coloring
clique, line graph, Extremal problems in graph theory, Vertex subsets with special properties (dominating sets, independent sets, cliques, etc.), FOS: Mathematics, Mathematics - Combinatorics, Combinatorics (math.CO), Reed's conjecture, coloring
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