1. Birrel, N.D., Davies, P.C.W.: Quantum Fields in Curved Space, (Cambridge Monographs on Mathematical Physics, Cambridge, 1994)
2. Cartan, E.: C. R. Acad. Sci. 174, 593 (1922), On Manifolds with an Affine Connection and the Theory of General Relativity, translated by A. Magnon and A. Ashtekar (Bibliopolis, Napoli, 1986)
3. Deser, S., van Nieuwenhuizen, P.: Phys. Rev. D10, 40 (1974), ibid 411
4. Deser, S., van Nieuwenhuizen P., Tsao, H.S.: Phys. Rev. D10, 3337 (1974)
5. Dirac, P.A.M.: Proc. Roy. Soc. Lond. A333, 403 (1973)