On k-wise intersecting families of vertex sets in perfect matchings

Abstract

We consider the following generalization of the seminal Erd\H{o}s-Ko-Rado theorem, due to Frankl. For k>= 2, let F be a k-wise intersecting family of r-subsets of an n element set X, i.e. any k sets in F have a nonempty intersection. If r<= (k-1/k)n, then |F|<={n-1 \choose r-1}. We extend Frankl's theorem in a graph-theoretic direction. For a graph G, and r>=1, let P^r(G) be the family of all r-subsets of the vertex set of G such that every r-subset is either an independent set or contains a maximum independent set. We will consider k-wise intersecting subfamilies of this family for the graph M_n, where M_n is the perfect matching on 2n vertices, and prove an analog of Frankl's theorem. This result can also be considered as an extension of a theorem of Bollob\'as and Leader for intersecting families of independent vertex sets in M_n.