1. Institut supérieur de Mathématiques Appliquées et de l'Informatique, Kairouan, Tunisia
2. Mathematics Department, Abdus Salam International Centre for Theoretical Physics, Trieste, Italy
3. ANLIG, UR13ES32, Faculty of Sciences of Tunis, Elmanar University, Tunis, Tunisia
4. Mathematics Department, Faculty of Sciences and Arts, King Khalid University, Muhayil Asir, Saudi Arabia
5. AGTS, LR11ES53, Universite de Sfax, Sfax, Tunisia