1. Mathisson, M. (1937).Acta Phys. Polon.,6, 163.
2. Einstein, A., Infeld, L., and Hoffmann, B. (1938).Ann. Math.,39, 65.
3. Fock, V. A. (1939).J. Phys. USSR,1, 81; (1964).The Theory of Space Time and Gravitation, 2nd revised ed. (Macmillan, New York).
4. Papapetrou, A. (1951).Proc. Phys. Soc.,64, 57.
5. Papapetrou, A. (1951).Proc. R. Soc. London,A209, 248.