Affiliation: | (1) Department of Computer Science, University of Toronto, M5S 1A4 Toronto, Ontario, Canada;(2) Computer and Intelligent Systems Laboratory, GTE Laboratories Incorporated, 40 Sylvan Road, 02254 Waltham, MA, U.S.A.;(3) Department of Computer Science, University of Toronto, M5S 1A4 Toronto, Ontario, Canada |