English

An improved threshold for the number of distinct intersections of intersecting families

Combinatorics 2022-11-23 v2

Abstract

A family F\mathcal{F} of subsets of {1,2,,n}\{1,2,\ldots,n\} is called a tt-intersecting family if FGt|F\cap G| \geq t for any two members F,GFF, G \in \mathcal{F} and for some positive integer tt. If t=1t=1, then we call the family F\mathcal{F} to be intersecting. Define the set I(F)={FG:F,GF and FG}\mathcal{I}(\mathcal{F}) = \{F\cap G: F, G \in \mathcal{F} \text{ and } F \neq G\} to be the collection of all distinct intersections of F\mathcal{F}. Frankl et al. proved an upper bound for the size of I(F)\mathcal{I}(\mathcal{F}) of intersecting families F\mathcal{F} of kk-subsets of {1,2,,n}\{1,2,\ldots,n\}. Their theorem holds for integers n50k2n \geq 50 k^2. In this article, we prove an upper bound for the size of I(F)\mathcal{I}(\mathcal{F}) of tt-intersecting families F\mathcal{F}, provided that nn exceeds a certain number f(k,t)f(k,t). Along the way we also improve the threshold k2k^2 to k3/2+o(1)k^{3/2+o(1)} for the intersecting families.

Keywords

Cite

@article{arxiv.2211.11341,
  title  = {An improved threshold for the number of distinct intersections of intersecting families},
  author = {Jagannath Bhanja and Sayan Goswami},
  journal= {arXiv preprint arXiv:2211.11341},
  year   = {2022}
}

Comments

Some errors in the previous draft have been corrected