1. Department of Mathematics, King Abdulaziz University, Science Faculty for Girls, P.O. Box 4087, Jeddah 21491, Saudi Arabia
2. Department of Mathematics, King Abdulaziz University, P.O. Box 80203, Jeddah 21859, Saudi Arabia
3. DEIM, Università Degli Studi di Palermo, Viale Delle Scienze, 90128 Palermo, Italy