1. Wu, T.T., Yang, C.N.: Phys. Rev. D12, 3843?3844 (1975); Gu, C.H., Yang, C.N.: Sci. Sin.18, 484 (1975); Gu, C.H., Yang, C.N.: Sci. Sin.20, 48 (1977); Deser, S., Wilczek, F.: Phys. Lett.65 B, 391?393 (1976); Deser, S., Drechsler, W.: Phys. Lett.86 B, 189?192 (1979); Roskies, R.: Phys. Rev. D15, 1731?1732 (1977); Calvo, M.: Phys. Rev. D15, 1733?1735 (1977); Halpern, M.B.: Phys. Rev. D16, 1798?1801 (1977); Halpern, M.B.: Nucl. Phys. B139, 477?489 (1878); Coleman, S.: Phys. Lett.70 B, 59?60 (1978); Bollini, C.G., Giambiagi, J.J., Tiomno, J.: Preprint A-0022/78. Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro RJ, Brazil; Bollini, C.G., Giambiagi, J.J., Tiomno, J.: Phys. Lett.83 B, 185?187 (1979); Solomon, S.: Nucl. Phys. B147, 174?188 (1979); Mostow, M.: Commun. Math. Phys.78, 137?150 (1980); Doria, F.A.: On an example of field copies by Deser and Wilczek. Dept. of Mathematics, Univ. of Rochester (1980)
2. Wu, T.T., Yang, C.N.: Phys. Rev. D12, 3843?3845 (1975)
3. Bollini, C.G., Giambiagi, J.J., Tiomno, J.: Preprint A-0022/78. Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro RJ, Brazil
4. Cho, Y.M.: J. Math. Phys.16, 2029?2035 (1975)
5. Kobayashi, S., Nomizu, K.: Foundations of differential geometry. I. New York, London: Interscience 1963; Sternberg, S.: Lectures on differential geometry. Englewood Cliffs, N.J.: Prentice-Hall 1964