1. Hehl, F. W., Ne'eman, Y., Nitsch, J., and Von der Heyde, P. (1978).Phys. Lett.,78B, 102?106. For more detail, see Hehl, F. W., Nitsch, J., and Von der Heyde, P. (1980). InGeneral Relativity and Gravitation, One Hundred Years After the Birth of Albert Einstein, Volume 1 (ed. A. Held), Plenum Press, New York, pp. 329?355.
2. Von der Heyde, P. (1976).Phys. Lett.,58A, 141?143;Z.Naturforsch.,31a, 1725?1726; Yasskin, P. B. (1979). Ph.D. thesis, University of Maryland.
3. Schweizer, M., and Straumann, N. (1979).Phys. Lett.,71A, 493?495; Smalley, L. L. (1980).Phys. Rev. D,21, 328?331; Nitsch, J., and Hehl, F. W. (1980).Phys. Lett.,90B, 98?102.
4. Eddington, A. S. (1924).The Mathematical Theory of Relativity, Cambridge University Press, Cambridge, pp. 141?144.
5. Lichnerowicz, A. (1958).C.R. Acad. Sci. (Paris),247, 433?436; Kilmister, C. W., and Newman, D. J. (1961).Proc. Cambridge Philos. Soc.,57, 851?864; Yang, C. N. (1974).Phys. Rev. Lett.,33, 445?447.