English

Triangles in intersecting families

Combinatorics 2022-01-12 v2

Abstract

We prove the following the generalized Tur\'an type result. A collection T\mathcal{T} of rr sets is an rr-triangle if for every T1,T2,,Tr1TT_1,T_2,\dots,T_{r-1}\in \mathcal{T} we have i=1r1Ti\cap_{i=1}^{r-1}T_i\neq\emptyset, but TTT\cap_{T\in \mathcal{T}}T is empty. A family F\mathcal{F} of sets is rr-wise intersecting if for any F1,F2,,FrFF_1,F_2,\dots,F_r\in \mathcal{F} we have i=1rFi\cap_{i=1}^rF_i\neq \emptyset or equivalently if F\mathcal{F} does not contain any mm-triangle for m=2,3,,rm=2,3,\dots,r. We prove that if nn0(r,k)n\ge n_0(r,k), then the rr-wise intersecting family F([n]k)\mathcal{F}\subseteq \binom{[n]}{k} containing the most number of (r+1)(r+1)-triangles is isomorphic to {F([n]k):F[r+1]r}\{F\in \binom{[n]}{k}:|F\cap [r+1]|\ge r\}.

Keywords

Cite

@article{arxiv.2201.02452,
  title  = {Triangles in intersecting families},
  author = {Dániel T. Nagy and Balázs Patkós},
  journal= {arXiv preprint arXiv:2201.02452},
  year   = {2022}
}

Comments

7 pages

R2 v1 2026-06-24T08:42:48.729Z