1. Salomon Brothers Int. Ltd. Victoria Plaza 111 Buckingham Palace Road London SWIW 0SB, UK
2. Department of Computer Science Rice University Houston, TX 77005-1892
3. Department of Computer Science Stanford University Stanford, CA 94305, USA
4. Department of Computer Science National Chengchi University Wenshan, Taipei, Taiwan
5. IBM Almaden Research Center San Jose, CA 95120, USA