1. Department of Mathematics; Government College University; Katchery Road Lahore 54000 Pakistan
2. Department of Mathematics; King Abdulaziz University; Jeddah 21589 Saudi Arabia
3. Department of Mathematics; University of Jeddah; P.O. Box. Jeddah 21589 Saudi Arabia
4. Department of Mathematics; COMSATS Institute of Information Technology; Abbottabad 22060 Pakistan