English

A simple proof of Talbot's theorem for intersecting separated sets

Combinatorics 2020-12-08 v2

Abstract

A subset AA of [n]={1,,n}[n] = \{1, \dots, n\} is kk-separated if, when the elements of [n][n] are considered on a circle, between any two elements of AA there are at least kk elements of [n][n] that are not in AA. A family A\mathcal{A} of sets is intersecting if every two sets in A\mathcal{A} intersect. We give a short and simple proof of a remarkable result of Talbot (2003), stating that if n(k+1)rn \geq (k + 1)r and A\mathcal{A} is an intersecting family of kk-separated rr-element subsets of [n][n], then A(nkr1r1)|\mathcal{A}| \leq \binom{n - kr - 1}{r - 1}. This bound is best possible.

Keywords

Cite

@article{arxiv.2008.02342,
  title  = {A simple proof of Talbot's theorem for intersecting separated sets},
  author = {Peter Borg and Carl Feghali},
  journal= {arXiv preprint arXiv:2008.02342},
  year   = {2020}
}

Comments

6 pages; expanded on the introduction

R2 v1 2026-06-23T17:40:06.248Z