1. Adler R., Bazin M., Schiffer M., Introduction to General Relativity, McGraw-Hill, Inc. (1975).
2. Noerdlinger P. D., Geodesics of Robertson-Walker Universes, Physical Review, Volume 186(5), pp. 1347 – 1351 (1969).
3. Mazilu N., (a) The Physical Basis of Procopiu’s Quantization, to appear in Memoirs of the Scientific Sections of the Romanian Academy, Tome XLVI; prepublished at viXra:2308.0135v1; (b) The Instanton: a Conspicuous Case of Scale Transition, to be published (2023).
4. Einstein A., (a) A New Formal Interpretation of Maxwell’s Field Equations of Electrodynamics, English translation of the German original from Sitzungsberichte der Preussischen Akademie der Wissenschaften, 1916, pp. 184 – 188; reproduced in The Collected Papers of Albert Einstein, Volume 6, Princeton University Press, as Document 27; (b) The Foundation of the General Theory of Relativity, English translation of the German original from Annalen der Physik, Volume 49, pp. 769 – 822; reproduced in The Collected Papers of Albert Einstein, Volume 6, Princeton University Press, as Document 30 (1916).
5. Einstein A., Cosmological Considerations on the General Theory of Relativity, in The Principle of Relativity, a Collection of Original Memoirs on the Special and General Theory of Relativity, Dover Publications, 1923, 1952, 2003, English translation of the German original from Sitzungsberichte der Preussischen Akademie der Wissenschaften, 1917 (1917).