1. S. Weinberg, Rev. Mod. Phys. 61, 1 (1989).
2. A. Einstein, Sitzungsber. Preuss. Akad. Wiss. phys.-math. Klasse VI, 142 (1917). See also: Ref. [2], Vol. 6, p. 540, Doc. 43.
3. A. Einstein, The Collected Papers of Albert Einstein. Princeton University Press; Vol. 8, Part A, p. 386, Doc. 294.
4. A. Pais, `Subtle is the Lord…’: The Science and the Life of Albert Einstein. Oxford University Press (1982). See especially Sect. 15e.
5. W. de Sitter, Proc. Acad. Sci., 19, 1217 (1917); and 20, 229 (1917).