1. COATI Joint Project CNRS-Inria-UNS; 2004 Route des Lucioles, BP 93 , F-06902 Sophia Antipolis France
2. Inria and LIRMM; CNRS-University of Montpellier; 860 Rue Saint Priest, F-34095 Montpellier Cedex 5 France
3. Inria Sophia Antipolis-Méditerranée; 2004 Route des Lucioles, BP 93, F-06902 Sophia Antipolis France
4. Department of Mathematics; UFV; Abbotsford BC Canada