Laboratory of Applied Mathematics, Badji-Mokhtar University, BP 12, Annaba 23000, Algeria
Bedr'Eddine Ainseba
Institute of Mathematics of Bordeaux, UMR CNRS 52 51, Case 36 Université Victor Segalen Bordeaux 2, 3 ter place de la Victoire, F 33076 Bordeaux Cedex, France