E. Fox, G. Nunn, and W. Lee. Proceedings of the 11th Annual International ACM SIGIR Conference on Research and Development in Information Retrieval, page 291-307. ACM Press, (1988)
Y. Kodratoff. Foundations of Intelligent Systems, 11th International Symposium, ISMIS '99, Proceedings, volume 1609 of Lecture Notes in Computer Science, page 16-29. Springer, (1999)
F. Jiang, and M. Littman. Proceedings of the Seventeenth International Conference on Machine Learning, page 423-430. Morgan Kaufmann Publishers Inc., (2000)