Paper detail

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

A subset of a group G of Sym(n) is intersecting if for any pair of permutations $π,σ\in G$ there is an $i$ in {1,2,...,n} such that $π(i) = σ(i)$. 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.