1. Laboratory of PDE’s, Algebra and Spectral Geometry, Department of Mathematics, Ibn Tofail University, FS, BP 133, Kénitra, Morocco
2. Mathematics Department, Faculty of Sciences Semalalia, Cadi Ayyad University, Boulevard Prince Moulay Abdellah, P. O. Box 2390, Marrakesh 40000, Morocco
3. Department of Mathematics, Linnæus University, 351 95 Växjö, Sweden
4. Matematik Bölümü Nevşehir Haci, Bektaş Veli Üniversitesi, Turkey