English

A note on two-colorability of nonuniform hypergraphs

Combinatorics 2021-12-17 v1 Discrete Mathematics Data Structures and Algorithms

Abstract

For a hypergraph HH, let q(H)q(H) denote the expected number of monochromatic edges when the color of each vertex in HH is sampled uniformly at random from the set of size 2. Let smin(H)s_{\min}(H) denote the minimum size of an edge in HH. Erd\H{o}s asked in 1963 whether there exists an unbounded function g(k)g(k) such that any hypergraph HH with smin(H)ks_{\min}(H) \geq k and q(H)g(k)q(H) \leq g(k) is two colorable. Beck in 1978 answered this question in the affirmative for a function g(k)=Θ(logk)g(k) = \Theta(\log^* k). We improve this result by showing that, for an absolute constant δ>0\delta>0, a version of random greedy coloring procedure is likely to find a proper two coloring for any hypergraph HH with smin(H)ks_{\min}(H) \geq k and q(H)δlogkq(H) \leq \delta \cdot \log k.

Keywords

Cite

@article{arxiv.1803.03060,
  title  = {A note on two-colorability of nonuniform hypergraphs},
  author = {Lech Duraj and Grzegorz Gutowski and Jakub Kozik},
  journal= {arXiv preprint arXiv:1803.03060},
  year   = {2021}
}
R2 v1 2026-06-23T00:46:24.829Z