1. Dept. Computer Science, King's College London, London WC2R 2LS, England
2. School of Computing, Curtin University of Technology, GPO Box 1987 U, WA, Australia
3. New Jersey Institute of Technology College of Computing Sciences 323 M.L.King Blvd., University Heights Newark, NJ 07102-1982, USA
4. Institut Gaspard-Monge, Université de Marne-la-Vallée, Cité Descartes, Champs sur Marne, 77454 Marne-la-Vallée CEDEX 2, France
5. Department of Computer Science, University of Pisa, Italy
6. New Jersey Institute of Technology College of Computing Sciences 323 M.L.King Blvd., University Heights Newark, NJ 07102-1982, USA
7. Inria Rhône-Alpes, UMR 5558 Biométrie et Biologie Évolutive Université Claude Bernard, Lyon 1. 43, Bd du 11 novembre 1918 69622 Villeurbanne cedex, France