G.S. Mokaddis, M. Salah EL-Sherbeny and Y. Mahmoud Ayid
Journal of Mathematics and Statistics 5 ( 1 ): 42 - 46 , 2009
G.S. Mokaddis, M. Salah EL-Sherbeny and Entesar Al-Esayeh
Journal of Mathematics and Statistics 5 ( 2 ): 112 - 117 , 2009