M. Croitoru, E. Compatangelo, and C. Mellish. Proceedings of the 13th International Conference on Conceptual Structures (ICCS 2005), volume 3596 of Lecture Notes in Computer Science, page 267-280. Springer, (2005)
S. Gustafson, and W. Hsu. Genetic Programming, Proceedings of EuroGP'2001, volume 2038 of LNCS, page 291--301. Lake Como, Italy, Springer-Verlag, (18-20 April 2001)