1. Einstein A., Grossmann M.: Outline of a generalized theory of relativity and of a theory of gravitation. In: Beck, A., Howard, D. (eds) The Collected Papers of Albert Einstein, vol. 4. The Swiss Years: Writings, 1912–1914, English Translation. The Hebrew University of Jerusalem and Princeton University, Princeton, 1996. Translated from Entwurf einer verallgemeinerten Relativitätstheorie und einer Theorie der Gravitation, Teubner, Leipzig (1913)
2. Norton J.: How Einstein found his field equations, 1912–1915. In: Howard, D., Stachel, J. (eds) Einstein and the History of General Relativity, Einstein Studies, vol. 1, pp. 101. Birkhäuser, Boston (1989)
3. Janssen M.: Of pots and holes: Einstein’s bumpy road to general relativity. Annalen der Physik 14(Suppl), 58 (2005)
4. Janssen M., Renn J.: Untying the knot: how Einstein found his way back to field equations discarded in the Zurich notebook. In: Renn, J. (eds) The Genesis of General Relativity, vol. 2: Einstein’s Zurich Notebook: Commentary and Essays, pp. 839–925. Springer, Dordrecht (2007)
5. Fletcher J.G.: Local conservation laws in generally covariant theories. Rev. Mod. Phys. 32, 65 (1960)