Affiliation: | a Computer Science Department, Australian National University, Canberra, ACT 0200, Australia b Department of Mathematics, Michigan State University, East Lansing, MI 48824-1027, USA c Department of Combinatorics and Optimization, Faculty of Mathematics, University of Waterloo, Waterloo, Ont., Canada N2L 3G1 d Computer Science Department, University of Georgia, Athens, GA 30602-7404, USA |