1. Rosen, N. (1973).Gen. Rel. Grav.,4, 435.
2. Rosen, N. (1974).Ann. Phys. N.Y.,84, 455.
3. Rosen, N. (1978).Gen. Rel. Grav.,9, 339.
4. Yano, K. (1965).The Theory of Lie Derivatives and its Applications. (North-Holland Publ. Co., Amsterdam).
5. Petrov, A. Z. (1969).Einstein Spaces (Pergamon Press, New York).