An Erdős-Ko-Rado type theorem for subgraphs of perfect matchings

Abstract

Let $M_k$ be a $2n$-vertex graph with $n$ pairwise disjoint edges and let ${\mathcal{H}}^{(p,s)}(n)$ be the family of subsets of $V(M_n)$ that span exactly $p$ edges and $s$ isolated vertices. We prove that for $n\ge 2p+s$ this family has the Erdős--Ko--Rado property: the size of the largest intersecting family equals to the number of sets containing a fixed vertex. The bound $n\ge 2p+s$ is the best possible, improving a recent theorem with $n\ge 2p+2s$ by Fuentes and Kamat.

4 pages