Cross-Intersecting Families of Vectors

János Pach, Gábor Tardos

Research output: Article

6 Citations (Scopus)


Given a sequence of positive integers p=(p1,…,pn), let Sp denote the family of all sequences of positive integers x=(x1,…,xn) such that xi≤pi for all i. Two families of sequences (or vectors), A, B⊆Sp, are said to be r-cross-intersecting if no matter how we select x∈A and y∈B, there are at least r distinct indices i such that xi=yi. We determine the maximum value of |A|·|B| over all pairs of r-cross-intersecting families and characterize the extremal pairs for r≥1, provided that min pi>r+1. The case min pi≤r+1 is quite different. For this case, we have a conjecture, which we can verify under additional assumptions. Our results generalize and strengthen several previous results by Berge, Borg, Frankl, Füredi, Livingston, Moon, and Tokushige, and answers a question of Zhang.

Original languageEnglish
Pages (from-to)477-495
Number of pages19
JournalGraphs and Combinatorics
Issue number2
Publication statusPublished - márc. 1 2015


ASJC Scopus subject areas

  • Theoretical Computer Science
  • Discrete Mathematics and Combinatorics

Cite this