1. Department of Mathematics, Faculty of Sciences and Technologies, Moulay Ismail University of Meknes, P.O. Box 509, Erachidia 52000, Morocco.
2. Department of Mathematics, Faculty Polydisciplinary of Larache, Abdelmalek Essaadi University, P.O. Box 745, Larache 92004, Morocco.
3. Department of Mathematics, Faculty of Sciences and Technologies, Moulay Ismail University of Meknes, P.O. Box 509, Errachidia, Morocco