Intersecting Systems

  • Authors:
  • R. Ahlswede;N. Alon;P. L. Erdös;M. Ruszinkó;L. A. Székely

  • Affiliations:
  • Fakultät für Mathematik, Universität Bielefeld, P.O. Box 100131, D-33501 Bielefeld 1, Germany;Department of Mathematics, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv, Israel (e-mail: noga@math.tau.ac.il);Mathematical Institute of the Hungarian Academy of Sciences, Budapest, P.O. Box 127, 1364 Hungary (e-mail: elp@math-inst.hu);Computer and Automation Research Institute of the Hungarian Academy of Sciences, Budapest, P.O. Box 63, 1518 Hungary (e-mail: ruszinko@lutra.sztaki.hu);Department of Computer Science, Eötvös University, Budapest, 1088 Hungary (e-mail: szekely@cs.elte.hu)

  • Venue:
  • Combinatorics, Probability and Computing
  • Year:
  • 1997

Quantified Score

Hi-index 0.00

Visualization

Abstract

An intersecting system of type (∃, ∀, k, n) is a collection 𝔽={ℱ1, ..., ℱm} of pairwise disjoint families of k-subsets of an n-element set satisfying the following condition. For every ordered pair ℱi and ℱj of distinct members of 𝔽 there exists an A∈ℱi that intersects every B∈ℱj. Let In (∃, ∀, k) denote the maximum possible cardinality of an intersecting system of type (∃, ∀, k, n). Ahlswede, Cai and Zhang conjectured that for every k≥1, there exists an n0(k) so that In (∃, ∀, k)=(n−1/k−1) for all nn0(k). Here we show that this is true for k≤3, but false for all k≥8. We also prove some related results.