English

Size, diversity, minimum degree, sturdiness, d\"omd\"od\"om

Combinatorics 2025-01-14 v2

Abstract

For a family F\mathcal{F} of sets and a disjoint pair A,BA,B we let F(A,B)={FF:AF, BF=}\mathcal{F}(A,\overline{B})=\{F\in \mathcal{F}: A\subseteq F, ~B\cap F=\emptyset\}. The \textbf{(p,q)(p,q)-d\"omd\"od\"om} of a family F2[n]\mathcal{F}\subseteq 2^{[n]} is βp,q(F)=min{F(A,B):A=p,B=q,AB=,A,B[n]}\beta_{p,q}(\mathcal{F})=\min\{|\mathcal{F}(A,\overline{B})|:|A|=p,|B|=q, A\cap B=\emptyset, A,B\subseteq [n]\} . This definition encompasses size, diversity, minimum degree, and sturdiness as special cases. We investigate the maximum possible value βp,q(n,k)\beta_{p,q}(n,k) of βp,q(F)\beta_{p,q}(\mathcal{F}) over all kk-uniform intersecting families F2[n]\mathcal{F}\subset 2^{[n]}. We determine the order of magnitude of βp,q(n,k)\beta_{p,q}(n,k) for all fixed p,q,kp,q,k. We relate the asymptotics of βp,q(n,k)\beta_{p,q}(n,k) to the constant value of β0,q(n,q+1)\beta_{0,q}(n,q+1) and establish βp,1(n,k)=(n3pk2p)\beta_{p,1}(n,k)=\binom{n-3-p}{k-2-p} and βp,2(n,k)=2(n5k3p)(n7k5p)\beta_{p,2}(n,k)=2\binom{n-5}{k-3-p}-\binom{n-7}{k-5-p} if nn is large enough.

Keywords

Cite

@article{arxiv.2501.02596,
  title  = {Size, diversity, minimum degree, sturdiness, d\"omd\"od\"om},
  author = {Balázs Patkós},
  journal= {arXiv preprint arXiv:2501.02596},
  year   = {2025}
}

Comments

6 pages

R2 v1 2026-06-28T20:56:51.335Z