1. Rolf Brandl and Libero Verardi, Finite simple groups with few conjugacy classes of subgroups, Japan. J. Math. (N.S.) 18 (1992), no. 2, 347–359.[MR]
  2. Libero Verardi, Matrices, graphs and equivalence relations, Ann. Mat. Pura Appl. (4) 180 (2002), no. 4, 413–428.[MR]