Intersecting hypergraphs with large cover number
Combinatorics
2025-04-15 v2
Abstract
In their famous 1974 paper introducing the local lemma, Erd\H{o}s and Lov\'asz posed a question-later referred by Erd\H{o}s as one of his three favorite open problems: What is the minimum number of edges in an -uniform, intersecting hypergraph with cover number ? This question was solved up to a constant factor in Kahn's remarkable 1994 paper. More recently, motivated by applications to Bollob\'as' ''power of many colours'' problem, Alon, Buci\'c, Christoph, and Krivelevich introduced a natural generalization by imposing a space constraint that limits the hypergraph to use only vertices. In this note we settle this question asymptotically, up to a logarithmic factor in in the exponent, for the entire range.
Cite
@article{arxiv.2503.14918,
title = {Intersecting hypergraphs with large cover number},
author = {Matija Bucić and Vanshika Jain and Varun Sivashankar},
journal= {arXiv preprint arXiv:2503.14918},
year = {2025}
}