1. M. A. Seoud:
Department of Mathematics, Faculty of Science, Ain Shams University Abbassia, Cairo, EGYPT
2. E. I. Abdel Maqsoud:
Department of Mathematics, Faculty of Science, Ain Shams University Abbassia, Cairo, EGYPT
3. A Y. I. Aldiban:
Department of Mathematics, Faculty of Science, Ain Shams University Abbassia, Cairo, EGYPT