1. Ellis, G. F. R.: 1971, in R. K. Sachs (ed.),General Relativity and Cosmology, Academic Press, New York, p. 117.
2. Landau, L. D. and Lifshitz, E. M.: 1963,Fluid Mech., Pergamon Press, Oxford; Vol.6, p. 505.
3. Lichnerowicz, A.: 1967,Relativistic Hydrodynamics and Magnetohydrodynamics, W. A. Benjamin Inc., New York, p. 63.
4. Misner, C. W.: 1967,Nature 214, 40.
5. Misner, C. W.: 1968,Astrophys. J. 151, 431.