M. Zahran, A. Wahab, and S. Shaheen. Proceedings of the Genetic and Evolutionary
Computation Conference, 1, page 814. Orlando, Florida, USA, Morgan Kaufmann, (13-17 July 1999)
B. Zhang, Y. Chen, W. Fan, E. Fox, M. Goncalves, M. Cristo, and P. Calado. Proceedings of the 28th Annual International ACM SIGIR
Conference on Research and Development in Information
Retrieval, page 667--668. Salvador, Brazil, ACM Press, (August 2005)