English

Idealness of $k$-wise intersecting families

Combinatorics 2020-10-06 v4 Discrete Mathematics

Abstract

A clutter is \emph{kk-wise intersecting} if every kk members have a common element, yet no element belongs to all members. We conjecture that, for some integer k4k\geq 4, every kk-wise intersecting clutter is non-ideal. As evidence for our conjecture, we prove it for k=4k=4 for the class of binary clutters. Two key ingredients for our proof are Jaeger's 88-flow theorem for graphs, and Seymour's characterization of the binary matroids with the sums of circuits property. As further evidence for our conjecture, we also note that it follows from an unpublished conjecture of Seymour from 1975. We also discuss connections to the chromatic number of a clutter, projective geometries over the two-element field, uniform cycle covers in graphs, and quarter-integral packings of value two in ideal clutters.

Keywords

Cite

@article{arxiv.1912.00614,
  title  = {Idealness of $k$-wise intersecting families},
  author = {Ahmad Abdi and Gérard Cornuéjols and Tony Huynh and Dabeen Lee},
  journal= {arXiv preprint arXiv:1912.00614},
  year   = {2020}
}

Comments

20 pages, 2 figures. An extended abstract under the same title appeared in the 21st Conference in Integer Programming and Combinatorial Optimization