1. Department of Mathematics, Faculty of Science and Technology, University Moulay Ismaïl, Errachidia, Morocco;
2. Department of Mathematics, Faculty of Science and Technology of Fez, University S. M. Ben Abdellah Fez, Fes, Morocco;
3. Department of Mathematics, Faculty of Science, University Ibn Tofail, Kenitra, Morocco;
4. Department of Mathematics, Al Hussein Bin Talal University, Ma'an, Jordan