1. D. Hilbert, Nachr. Ges. Wiss. Goettingen, Math.-Phys. 23 (1916).
2. L. D. Landau and E. M. Lifshits, The Classical Theory of Field (Fizmatlit, Moscow, 2001; Pergamon Press, Oxford, 1975).
3. A. Einstein, “Bases of General Relativity”, in Collection of Scientific Works (Nauka, Moscow, 1965), Vol. I, pp. 452–504 [in Russian].
4. P. Painlevé, “La gravitation dans la Mécanique de Newton et dans la Mécanique d’Einstein,” Comptes rendus (Académie des sciences, 1921), Vol. 173,Issue 20, pp. 873–887; “Gravitation in Newtonian Mechanics and Einsteinian Mechanics,” Gravitatsiya 5 (1), 16–27 (2001).
5. A. Einstein, “On a Stationary Systems with Spherical Symmetry Consisting of Many Gravitating Masses,” in Collection of Scientific Works (Nauka, Moscow, 1966), Vol. 2, pp. 514–531 [in Russian]; “On a Stationary Systems with Spherical Symmetry Consisting of Many Gravitating Masses,” Ann. Math. 40, 922–936 (1939).