A note on random greedy coloring of uniform hypergraphs

Abstract

The smallest number of edges forming an n-uniform hypergraph which is not r-colorable is denoted by m(n,r). Erd\H{o}s and Lov\'{a}sz conjectured that m(n,2)=\theta(n 2^n)$. The best known lower bound m(n,2)=\Omega(sqrt(n/log(n)) 2^n) was obtained by Radhakrishnan and Srinivasan in 2000. We present a simple proof of their result. The proof is based on analysis of random greedy coloring algorithm investigated by Pluh\'ar in 2009. The proof method extends to the case of r-coloring, and we show that for any fixed r we have m(n,r)=\Omega((n/log(n))^(1-1/r) r^n) improving the bound of Kostochka from 2004. We also derive analogous bounds on minimum edge degree of an n-uniform hypergraph that is not r-colorable.