Structure and properties of large intersecting families
Abstract
We say that a family of -subsets of an -element set is intersecting, if any two of its sets intersect. In this paper we study different extremal properties of intersecting families, as well as the structure of large intersecting families. We also give some results on -uniform families without pairwise disjoint sets, related to the Erd\H{o}s Matching Conjecture. We prove a conclusive version of Frankl's theorem on intersecting families with bounded maximal degree. This theorem, along with its generalizations to cross-intersecting families, implies many results on the topic, obtained by Frankl, Frankl and Tokushige, Kupavskii and Zakharov and others. We study the structure of large intersecting families, obtaining some general structural theorems which generalize the results of Han and Kohayakawa, as well as Kostochka and Mubayi. We give degree and subset degree version of the Erd\H{o}s--Ko--Rado and the Hilton--Milner theorems, extending the results of Huang and Zhao, and Frankl, Han, Huang and Zhao. We also extend the range in which the degree version of the Erd\H{o}s Matching conjecture holds.
Keywords
Cite
@article{arxiv.1710.02440,
title = {Structure and properties of large intersecting families},
author = {Andrey Kupavskii},
journal= {arXiv preprint arXiv:1710.02440},
year = {2019}
}
Comments
This is a preliminary version of the text, which I decided to keep because other papers refer to the problems I posed in this version. By now, it was split into two papers: arXiv:1810.00915 and arXiv:1810.00920 . The presentation was improved and the results concerning the structure of intersecting families were generalized and strengthened