English

Maximum size intersecting families of bounded minimum positive co-degree

Combinatorics 2021-03-08 v2

Abstract

Let H\mathcal{H} be an rr-uniform hypergraph. The \emph{minimum positive co-degree} of H\mathcal{H}, denoted by δr1+(H)\delta_{r-1}^+(\mathcal{H}), is the minimum kk such that if SS is an (r1)(r-1)-set contained in a hyperedge of H\mathcal{H}, then SS is contained in at least kk hyperedges of H\mathcal{H}. For rkr\geq k fixed and nn sufficiently large, we determine the maximum possible size of an intersecting rr-uniform nn-vertex hypergraph with minimum positive co-degree δr1+(H)k\delta_{r-1}^+(\mathcal{H}) \geq k and characterize the unique hypergraph attaining this maximum. This generalizes the Erd\H os-Ko-Rado theorem which corresponds to the case k=1k=1. Our proof is based on the delta-system method.

Keywords

Cite

@article{arxiv.2005.04282,
  title  = {Maximum size intersecting families of bounded minimum positive co-degree},
  author = {József Balogh and Nathan Lemons and Cory Palmer},
  journal= {arXiv preprint arXiv:2005.04282},
  year   = {2021}
}