English

Shattered matchings in intersecting hypergraphs

Combinatorics 2021-01-20 v1

Abstract

Let XX be an nn-element set, where nn is even. We refute a conjecture of J. Gordon and Y. Teplitskaya, according to which, for every maximal intersecting family F\mathcal{F} of n2\frac{n}2-element subsets of XX, one can partition XX into n2\frac{n}2 disjoint pairs in such a way that no matter how we pick one element from each of the first n21\frac{n}2 - 1 pairs, the set formed by them can always be completed to a member of F\mathcal{F} by adding an element of the last pair. The above problem is related to classical questions in extremal set theory. For any t2t\ge 2, we call a family of sets F2X\mathcal{F}\subset 2^X {\em tt-separable} if for any ordered pair of elements (x,y)(x,y) of XX, there exists FFF\in\mathcal{F} such that F{x,y}={x}F\cap\{x,y\}=\{x\}. For a fixed t,2t5t, 2\le t\le 5 and nn\rightarrow\infty, we establish asymptotically tight estimates for the smallest integer s=s(n,t)s=s(n,t) such that every family F\mathcal{F} with Fs|\mathcal{F}|\ge s is tt-separable.

Keywords

Cite

@article{arxiv.2005.04880,
  title  = {Shattered matchings in intersecting hypergraphs},
  author = {Peter Frankl and Janos Pach},
  journal= {arXiv preprint arXiv:2005.04880},
  year   = {2021}
}

Comments

12 pages

R2 v1 2026-06-23T15:26:46.294Z