Affiliation: | 1. Department of Mathematics, University of Nebraska—Lincoln, Lincoln, Nebraska 68588‐0130;2. Department of Communications and Networking, Helsinki University of Technology TKK, P.O. Box 3000, 02015 TKK, Finland;3. The University of Queensland, Department of Mathematics, Qld 4072, Australia;4. 4520 Mathematics Department, Illinois State University, Normal, Illinois 61790‐4520 |