1. Department of Mathematics, University of Peshawar, Peshawar, Khyber Pakhtunkhwa, Pakistan
2. Department of Mathematics, City University of Science and Information Technology, Peshawar, Khyber Pakhtunkhwa, Pakistan
3. Department of Mathematics and Statistics, York University, Toronto, ON M3J 1P3, Canada
4. Department of Mathematics and Statistics College of Science, King Faisal University, P. O. Box 400, Al Ahsa 31982, Saudi Arabia