1. G. Butler, S. S. Iyer, and E. A. O'Brien, A database of groups of prime-power order, Softw., Pract. Exper. 24 (1994), no. 10, 911-951.
  2. Gregory Butler, The maximal subgroups of the sporadic simple group of Held, J. Algebra 69 (1981), no. 1, 67–81.[MR]
  3. Gregory Butler and John J. Cannon, Cayley, Version 4: The user language, in ISSAC '88: Proceedings of the 1988 International Symposium on Symbolic and Algebraic Computation, vol. 358, Springer-Verlag, Berlin, 1988, pp. 456-466.