1. Department of Mathematics, King Saud University, P. O. Box 22452, Riyadh 11495, Saudi Arabia
2. Department of Mathematics, Government College University, Faisalabad 38600, Pakistan
3. Department of Mathematics, Government College Women University Faisalabad, Faisalabad 38600, Pakistan
4. University of Massachusetts Medical School, Worcester, MA 01655, USA
5. Department of Mathematics, Huzhou University, Huzhou 313000, P. R. China