1. Department of Mathematics, Faculty of Sciences, University of Tlemcen, Tlemcen, Algeria
2. Institut Camille Jordan, UMR 5208, CNRS, University Lyon 1, Villeurbanne, France
3. INRIA, Université de Lyon, Université Lyon 1, Institut Camille Jordan, Villeurbanne Cedex, France
4. Peoples Friendship University of Russia (RUDN University), Moscow, Russian Federation
5. Poncelet Center, UMI 2615, CNRS, Moscow, Russian Federation