1. Weyl, H. (1921).Raum-Zeit-Materie, 4th ed., Springer-Verlag, Berlin. [English translation: (1952).Space-Time-Matter, Dover, New York], Chap. IV.
2. Eddington, A. (1924).The Mathematical Theory of Relativity, 2nd ed., Chap. IV. Cambridge University Press.
3. Vermeil, H. (1917).Nachr. Ges. Wiss. Göttingen;334; see also Ref. [1], Appendix II; Cartan, (1922).E. J. de Math. Pures et Appl. 1, 141.
4. Weyl, H.Ann. Phys. 59, 101 (1919).
5. Pauli, W. (1921). (1921). inEncyklopädie der mathematischen Wissenschaften, Vol. V/2, B. G. Teubner, Leipzig [English translation (with supplementary notes): (1958).Theory of Relativity, Pergamon Press, New York], Sec. 65.