1. Mathematics Department, Faculty of Science, South Valley University, Qena, Egypt
2. Department of Mathematics and Statistics, Texas Tech University, Lubbock, TX 79409-1042, USA
3. Mathematics Department, College of Science and Humanities Studies in Al-Kharj, Prince Sattam bin Abdulaziz University, Al-Kharj 11942, Saudi Arabia
4. Department of Basic Science, Faculty of Computers and Informatics, Suez Canal University, Ismailia 41522, Egypt