Affiliation: | (1) Dept. of Combinatorics and Optimization, University of Waterloo, N2L 3G1 Waterloo, Ontario, CANADA;(2) Dept. of Alg., Combin. and Analysis, Auburn University, 36849-5307 Auburn, Alabama, U.S.A.;(3) Department of Mathematics, Emory University, 30322 Atlanta, Georgia, U.S.A. |