1. Faculty of Education, Department of Mathematics, Alexandria University, Alexandria, Egypt
2. Faculty of Science and Letter in Al Bukayriyyah, Department of Mathematics, Al-Qassim University, Al-Qassim, Saudi Arabia
3. Department of Mathematical Physical Sciences, Nizwa University, P.O. Box 1357, Nizwa-611, Oman
4. Arab Academy for Science and Technology, P.O. Box 1029, Alexandria, Egypt