1. Department of Mathematics, Faculty of Physical Sciences, Ahmadu Bello University, Zaria, Nigeria
2. Depart of Mathematics, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia
3. Department of Mathematics, Government College University, Faisalabad, Pakistan
4. Department of Mathematics, Çankaya University, Ankara, Turkey
5. Department of Medical Research, China Medical University Hospital, China Medical University, Taichung, Taiwan