1. LIFL, Universit de Lille, 59655 Villeneuve d'Ascq Cedex, France
2. Department of Computer Science, University of Tennessee, Knoxville, TN 37996-1301, USA
3. Mathematical Sciences Section, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
4. LIP, UMR CNRS-ENS Lyon-INRIA 8512, ENS Lyon, 69364 Lyon Cedex 07, France
5. ICPS, Universit de Strasboury, Pôle Api, 67400 Illkirch, France