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2. G. Cavalleri andG. Spinelli:Riv. Nuovo Cimento,3, No. 8 (1980).
3. For example in the Nordström theory, (G. Nordström:Phys. Z.,13, 1126 (1912)), the equations of motion of which cannot be obtained by a Lagrangian formulation (although its field equations can, as shown byS. Deser andL. Halpern:Gen. Rel. Grav.,1, 131 (1970)), the centre of mass of two attracting bodies should accelerate even if the system of the two bodies is isolated. This theoretical drawback was shown byG. J. Whitrow andG. E. Morduch: inVistas in Astronomy, Vol.6, edited byA. De Beer (London, 1965).
4. I. M. Khalatnikov:Ž. Ėksp. Teor. Fiz.,27, 529 (1954);L. Infeld:Bull. Acad. Pol. Sci. Cl. 3,5, 491 (1957);G. Kalman:Phys. Rev.,123, 384 (1961);G. Cavalleri andG. Spinelli:Lett. Nuovo Cimento,9, 325 (1974).
5. G. Cavalleri andG. Spinelli:Riv. Nuovo Cimento,3, 8 (1980), subsect.4’4.