1. Département de Mathématiques, Faculté des Sciences, Equipe d́équations fonctionnelles et Applications (EEFA), BP 8106, Agadir, Morocco
2. Department of Mathematics, Faculty of Science and Technology, Moulay Ismaïl University, Errachidia, Morocco
3. Department of Mathematics, College of Science, Taibah University, P. O. Box 2285 Madina, Saudi Arabia