1. Angeline, P.J. 1997. Subtree Crossover: Building block engine or macromutation? In Proceedings of GP'97, pages 9-17.

2. Collins, R. 1992. Studies in Artificial Life. PhD thesis. University of California, Los Angeles.

3. Francone F. D., Banzhaf W., Conrads M, Nordin P. 1999. Homologous Crossover in Genetic Programming. In Proceedings of the Genetic and Evolutionary Computation Conference, GECCO 99, pages 1021-1038.

4. Goldberg, David E. 1989. Genetic Algorithms in Search, Optimization and Machine Learning. Addison Wesley.

5. Keijzer M., Ryan C., O'Neill M., Cattolico M., Babovic V. 2001. Ripple Crossover in Genetic Programming. In Proceedings of EuroGP 2001.

6. Koza, J. 1992. Genetic Programming. MIT Press.

7. Langdon W.B. 1999. Size Fair and Homologous Tree Genetic Programming Crossovers. In Proceedings of the Genetic and Evolutionary Computation Conference, GECCO 99, pages 1092-1097.

8. Langdon W.B., Soule T., Poli R., and Foster J.A. 1999. The Evolution of Size and Shape. In Advances in Genetic Programming Volume 3, MIT Press 1999, pp 162-190.

9. O'Neill M. and Ryan C. 2001. Grammatical Evolution. IEEE Trans. Evolutionary Computation, 2001.

10. Justinian P. Rosca and Dana H. Ballard. 1999. Rooted-Tree Schemata in Genetic Programming, in Advances in Genetic Programming 3, Chapter 11, pp 243-271, 1999, MIT Press.

11. O'Neill M. and Ryan C. 2000. Crossover in Grammatical Evolution: A Smooth Operator? Lecture Notes in Computer Science 1802, Proceedings of the European Conference on Genetic Programming, pages 149-162. Springer-Verlag.

12. O'Neill M. and Ryan C. 1999. Genetic Code Degeneracy: Implications for Grammatical Evolution and Beyond. In Proceedings of the Fifth European Conference on Artificial Life.

13. O'Neill M. and Ryan C. 1999. Under the Hood of Grammatical Evolution. In Proceedings of the Genetic & Evolutionary Computation Conference 1999.

14. O'Neill M. and Ryan C. 1999. Evolving Multi-line Compilable C Programs. Lecture Notes in Computer Science 1598, Proceedings of the Second European Workshop on Genetic Programming, pages 83-92. Springer-Verlag.

15. Poli Riccardo, Langdon W.B. 1998. On the Search Properties of Different Crossover Operators in Genetic Programming. In Proceedings of the Third annual Genetic Programming conference 1998, pages 293-301.

16. Ryan C. and O'Neill M. 1998. Grammatical Evolution: A Steady State Approach. In Late Breaking Papers, Genetic Programming 1998, pages 180-185.

17. Ryan C., Collins J.J., and O'Neill M. 1998. Grammatical Evolution: Evolving Programs for an Arbitrary Language. Lecture Notes in Computer Science 1391, Proceedings of the First European Workshop on Genetic Programming, pages 8395. Springer-Verlag.