1. Arcidiacono, G.: 1986,Relativity, Cosmology and Gravitation, Hadronic Press, Massachusetts.
2. Arcidiacono, G.: 1988,Hadronic J. (U.S.A.) 12, 287.
3. Brans, C. and Dicke, R. H.: 1961,Phys. Rev. 124, 925.
4. Singh, R. S.: 1977, Ph.D. Thesis, Banaras Hindu University Varanasi, India.
5. Singh, T. and Arcidiacono, G.: 1989,A Birkhoff-Type Theorem in General Projective Relativity (communicated).