1. V. V. Narlikar, K. R. Karmarkar and F. A. Karmarkar, Proc. Ind. Acad. Sci.,B29, 91?97 (1949).
2. L. D. Landau and E. M. Lifshits, Field Theory [in Russian], Nauka, Moscow (1973).
3. H. Stephani, Gen. Relat. Gravit.,9, 789?792 (1978).
4. B. Carter, Black Holes (Les Houches Lectures 1972, B. DeWitt and D. DeWitt, eds.), Gordon and Breach, New York (1972), pp. 42?67.
5. J. M. Stewart and M. Walker, Black Holes: The Outside Story. Springer Tracts in Modern Physics,69, Springer Verlag, Berlin-Heidelberg-New York (1973).