English

On a conjecture of Szemer\'edi and Petruska

Combinatorics 2019-04-23 v2

Abstract

Consider a 33-uniform hypergraph of order nn with clique number kk such that the intersection of all its kk-cliques is empty. Szemer\'edi and Petruska proved n8m2+3mn\leq 8m^2+3m, for fixed m=nkm=n-k, and they conjectured the sharp bound n(m+22)n\leq{m+2\choose 2}. Tuza proved the best known bound, n34m2+m+1n\leq \frac{3}{4}m^2+m+1, using the machinery of τ\tau-critical hypergraphs. Here we propose an alternative approach, combining a decomposition process introduced by Szemer\'edi and Petruska with the skew version of Bollob\'as's theorem to prove nm2+6m+2n\leq m^2 + 6m + 2. While the bound obtained here is weaker than Tuza's bound, it is a proof-of-concept for a different approach and a call to apply dimension bounds from linear algebra.

Keywords

Cite

@article{arxiv.1904.04921,
  title  = {On a conjecture of Szemer\'edi and Petruska},
  author = {Adam S. Jobson and André E. Kézdy and Tim Pervenecki},
  journal= {arXiv preprint arXiv:1904.04921},
  year   = {2019}
}

Comments

9 pages, no figures: Version 2 reflects new information about the best known upper bound. We are very grateful to Zsolt Tuza for alerting us to the best known upper bound, $\frac{3}{4}m^2+m+1$, for the maximum order of a $\tau$-critical $3$-uniform hypergraph with transversal number $m$