1. Professor, Mathematics Dept., Faculty of Science, Al-Azhar Univ., Nasr City 11884, Cairo, Egypt; and Mathematics Dept., Faculty of Science, Taif Univ., Hawia (888) Taif, Saudi Arabia (corresponding author).
2. Dr., Mathematics Dept., Faculty of Science (Girls), Al-Azhar Univ., Nasr City 11884, Cairo, Egypt.