Mathematics Department;
Faculty of Science;
King Faisal University;
P.O.Box 380 Al-Ahsaa 31982;
the Kingdom of Saudi Arabia;
Department of Mathematics;
Faculty of Science;
Ain Shams University;
Cairo;
11566;
Egypt;
Center for Theoretical Physics;
British University of Egypt;
Sherouk City 11837;
P.O.Box 43;
Egypt;