English

Covers in Partitioned Intersecting Hypergraphs

Combinatorics 2015-01-05 v2

Abstract

Given an integer rr and a vector a=(a1,,ap)\vec{a}=(a_1, \ldots ,a_p) of positive numbers with ipai=r\sum_{i \le p} a_i=r, an rr-uniform hypergraph HH is said to be a\vec{a}-partitioned if V(H)=ipViV(H)=\bigcup_{i \le p}V_i, where the sets ViV_i are disjoint, and eVi=ai|e \cap V_i|=a_i for all eH,  ipe \in H,~~i \le p. A 1\vec{1}-partitioned hypergraph is said to be rr-partite. Let t(a)t(\vec{a}) be the maximum, over all intersecting a\vec{a}-partitioned hypergraphs HH, of the minimal size of a cover of HH. A famous conjecture of Ryser is that t(1)r1t(\vec{1})\le r-1. Tuza conjectured that if r>2r>2 then t(a)=rt(\vec{a})=r for every two components vector a=(a,b)\vec{a}=(a,b). We prove this conjecture whenever aba\neq b, and also for a=(2,2)\vec{a}=(2,2) and a=(4,4)\vec{a}=(4,4).

Keywords

Cite

@article{arxiv.1412.3067,
  title  = {Covers in Partitioned Intersecting Hypergraphs},
  author = {Ron Aharoni and C. J. Argue},
  journal= {arXiv preprint arXiv:1412.3067},
  year   = {2015}
}

Comments

4 pages

R2 v1 2026-06-22T07:25:33.461Z