English

A generalization of the Bollob\'as set pairs inequality

Combinatorics 2020-06-09 v2

Abstract

The Bollob\'as set pairs inequality is a fundamental result in extremal set theory with many applications. In this paper, for nkt2n \geq k \geq t \geq 2, we consider a collection of kk families Ai:1ik\mathcal{A}_i: 1 \leq i \leq k where Ai={Ai,j[n]:j[n]}\mathcal{A}_i = \{ A_{i,j} \subset [n] : j \in [n] \} so that A1,i1Ak,ikA_{1, i_1} \cap \cdots \cap A_{k,i_k} \neq \emptyset if and only if there are at least tt distinct indices i1,i2,,iki_1,i_2,\dots,i_k. Via a natural connection to a hypergraph covering problem, we give bounds on the maximum size βk,t(n)\beta_{k,t}(n) of the families with ground set [n][n].

Keywords

Cite

@article{arxiv.1812.00537,
  title  = {A generalization of the Bollob\'as set pairs inequality},
  author = {Jason O'Neill and Jacques Verstraete},
  journal= {arXiv preprint arXiv:1812.00537},
  year   = {2020}
}

Comments

Revised writing from previous version