Institution: | (1) Faculty of Science, Mathematics Department (Women’s Section), King Abdul-Aziz University, P.O. Box 41101, Jeddah, 21521, Saudi Arabia;(2) Faculty of Science, Mathematics Department, Ain Shams University, Cairo, Egypt;(3) Department of Mathematics and Physics, Manchester Metropolitan University, Manchester, M1 5GD, England;(4) Mathematics Department, UMIST, P.O. Box 88, Manchester, M60 1QD, England |