1. Dirac, P.A.M. (1973).Proc. R. Soc. London A,333, 403.
2. Hoyle, F., and Narlikar, J. V. (1974).Action at a Distance in Physics and Cosmology (Freeman, San Francisco).
3. Canuto, V., Adams, P. J., Hsieh, S.-H., and Tsiang, E. (1977).Phys. Rev. D,16, 1643.
4. Beckenstein, J. D. (1977).Phys. Rev. D,15, 1458.
5. Wesson, P. S. (1978).Cosmology and Geophysics (Hilger, Bristol, and Oxford University Press, New York).