The Erdős-Ko-Rado property for some 2-transitive groups

Abstract

A subset of a group G of Sym(n) is intersecting if for any pair of permutations $\pi ,\sigma \in G$ there is an $i$ in {1,2,...,n} such that $\pi (i)=\sigma (i)$. It has been shown, using an algebraic approach, that the largest intersecting sets in each of Sym(n), Alt(n) and PGL(2,q) are exactly the cosets of the point-stabilizers. In this paper, we show how this method can be applied more generally to many 2-transitive groups. We then apply this method to the Mathieu groups and to all 2-transtive groups with degree no more than 20.

arXiv comment20 pages