1. University of Tunis El ManarResearch Unity of Modeling in Fundamental Sciences and Didactics, IPEIEM, BP 254 El Manar 2 2096 Tunis Tunisia
2. University Paris DiderotSorbonne Paris Cite, ITODYS. UMR 7086 CNRS 15 rue J. A. de Baïf 75205 Paris Cedex 13 France.