1. Bergmann, P. G. (1982). InUnified Field Theories in More Than Four Dimensions, V. De Sebbata, and E. Schmutzer, eds., World Scientific, Singapore.
2. Boothby, W. M. (1975).An Introduction to Differentiable Manifolds and Riemannian Geometry, Academic Press, New York.
3. Dubois-Violette, M. (1983).Physics Letters,131B, 323.
4. Deser, S. (1970).General Relativity and Gravitation,1, 9.
5. Ellis, G., Sumeruk, A., Coule, D., and Hellaby, C. (1992).Classical and Quantum Gravity,9, 1535.