Affiliation: | Department of Computer Science, University of Toronto, Toronto, Ontario, Canada M5S 1A4;IBM Research Laboratory, 5600 Cottle Road, San Jose, California 95193, U.S.A.;Department of Computer Science, Cornell University, Ithaca, New York 14853, U.S.A.;Department of Computer Science, University of Washington, Seattle, Washington 98195, U .S.A. |