Intersecting families of sets and permutations : a survey

Abstract

A family A of sets is said to be t-intersecting if any two sets in A have at least t common elements. A central problem in extremal set theory is to determine the size or structure of a largest t-intersecting sub-family of a given family F. We give a survey of known results, conjectures and open problems for various important families F, namely, power sets, levels of power sets, hereditary families, families of signed sets, families of labeled sets, and families of permutations. We also provide some extensions and consequences of known results.