A. Agogino, K. Tumer, and R. Miikkulainen. GECCO'05: Proc. 7th Genetic and Evolutionary Computation Conf., page 1309--1316. Washington, DC, ACM Press, (2005)
J. Koza, S. Al-Sakran, and L. Jones. Genetic Programming Theory and Practice IV, volume 5 of Genetic and Evolutionary Computation, chapter 4, Springer, Ann Arbor, (11-13 May 2006)