1. R. Adler, M. Bazin andM. Schiffer:Introduction to General Relativity (New York, N. Y., 1965), p. 401.
2. R. Adler, M. Bazin andM. Schiffer:Introduction to General Relativity (New York, N. Y., 1965), p. 185, 186.
3. R. Adler, M. Bazin andM. Schiffer:Introduction to General Relativity (New York, N. Y., 1965), p. 204.
4. S. Weinberg:Gravitation and Cosmology: Principles and Application of the General Theory of Relativity (New York, N. Y., 1972), p. 198.