1. Afwat Abd El-Megid, M. El-Ghoul and A. El-Ahmady in “Second Conference on Operation Research and its Military Applications”, Egypt, 17–19 November 1987.
2. F. Brickell and R. S. Clark, “Differentiable manifolds” (Van Nostrand Reinhold, London, 1970).
3. M. El-Ghoul and A. E. El-Ahmady, in “Advances in modelling and analysis”, Vol. 4 (A. MSER, France, 1993) pp. 49–58.
4. Kentaro Yano, “Differential geometry on complex and almost complex spaces”, (Pergamon Press, New York 1964).
5. M. El-Ghoul, PhD thesis, Tanta University, Egypt (1985).