1. V. Fock, Contemporary Physics—Trieste Symp. 1968, Ed. A. Salam, Vol. 1., 511, IAEA, 1969.
2. W. de Sitter, Nature,128, 706, 1931.
3. M. J. Rees, Quantum Gravity 2, A Second Oxford Symp., Ed. C. J. Isham, R. Penrose, D. W. Sciama, Clarendon Press, Oxford, 1981, p. 273.
4. S. W. Hawking and G. F. R. Ellis, The Large Scale Structure of Space-Time, Cambridge Univ. Press, 1973.
5. A. Lichnerowicz, Théories relativités de la gravitation et de l’electromagnétisme, Masson, Paris, 1955.