An Erdos-Ko-Rado theorem for the derangement graph of PGL(2, q) acting on the projective line

作者：Meagher Karen^*; Spiga Pablo

来源：Journal of Combinatorial Theory - Series A, 2011, 118(2): 532-544.

DOI：10.1016/j.jcta.2010.11.003

• Derangement graph
• Independent sets
• Erdos-Ko-Rado theorem

Let G = PGL(2, q) be the projective general linear group acting on the projective line P(q). A subset S of G is intersecting if for any pair of permutations pi, sigma in S, there is a projective point p is an element of P(q) such that p(pi) = p(sigma). We prove that if S is intersecting, then vertical bar S vertical bar <= q(q - 1). Also, we prove that the only sets S that meet this bound are the cosets of the stabilizer of a point of P(q).

• 出版日期2011-2