English

The structure of maximal non-trivial d-wise intersecting uniform families with large sizes

Combinatorics 2023-06-08 v2

Abstract

For a positive integer d2d\geq 2, a family F([n]k)\mathcal F\subseteq \binom{[n]}{k} is said to be d-wise intersecting if F1F2Fd1|F_1\cap F_2\cap \dots\cap F_d|\geq 1 for all F1,F2,,FdFF_1, F_2, \dots ,F_d\in \mathcal F. A d-wise intersecting family F([n]k)\mathcal F\subseteq \binom{[n]}{k} is called maximal if F{A}\mathcal F\cup\{A\} is not d-wise intersecting for any A([n]k)FA\in\binom{[n]}{k}\setminus\mathcal F. We provide a refinement of O'Neill and Verstra\"{e}te's Theorem about the structure of the largest and the second largest maximal non-trivial d-wise intersecting k-uniform families. We also determine the structure of the third largest and the fourth largest maximal non-trivial d-wise intersecting k-uniform families for any k>d+14k>d+1\geq 4, and the fifth largest and the sixth largest maximal non-trivial 3-wise intersecting k-uniform families for any k5k\geq 5, in the asymptotic sense. Our proofs are applications of the Δ\Delta-system method.

Keywords

Cite

@article{arxiv.2207.01049,
  title  = {The structure of maximal non-trivial d-wise intersecting uniform families with large sizes},
  author = {Menglong Zhang and Tao Feng},
  journal= {arXiv preprint arXiv:2207.01049},
  year   = {2023}
}