J. Koza, W. Mydlowec, G. Lanza, J. Yu, and M. Keane. Proceedings of the Genetic and Evolutionary
Computation Conference (GECCO-2001), page 57--65. San Francisco, California, USA, Morgan Kaufmann, (7-11 July 2001)
J. Koza, L. Jones, M. Keane, and M. Streeter. Genetic Programming Theory and Practice II, chapter 8, Springer, Ann Arbor, pages missing?.(13-15 May 2004)