R. Cameron-Jones, and J. Quinlan. Proceedings of the 13th International Joint Conference on Artificial Intelligence, page 1050--1057. Morgan Kaufmann, (1993)
D. Shen, G. Kruijff, and D. Klakow. Natural Language Processing ? IJCNLP 2005: Second International Joint Conference, Jeju Island, Korea, October 11-13, 2005. Proceedings., Springer-Verlag, (2005)