1. Department of Mathematics, College of Science, King Saud University, P. O. Box 1142 Riyadh 11989, Saudi Arabia
2. Department of Mathematics, Gulbarga University, Gulbarga, India
3. Department of Mathematics, Faculty of Science, University of Jeddah, Jeddah 21589, Saudi Arabia
4. Department of Mathematics, Faculty of Education, Ain Shams University, Roxy 11757, Cairo, Egypt