1. A. Sandage, Astrophys. J.,202, 563, 1975.
2. S. J. Prokhovnik, Int. J. Th. Phys.,9, 291, 1974.
3. A. D. Allen, Found. Phys.,6, 59, 1976.
4. S. J. Prokhovnik, The Logic of Special Relativity. Cambridge University Press, Cambridge, 1967.
5. W. H. McCrea, Proc. Math. Soc. Univ. of Southampton,5, 15, 1962.