1. For recent reviews see the articles by B. Carter, S. Chandrasekhar, G. Gibbons, and S. W. Hawking in General Relativity: An Einstein Centenary Survey, edited by S. W. Hawking and W. Israel (Cambridge U.P., Cambridge, 1979).
2. See, for example, the article by S. Chandrasekhar in Ref. 1.
3. See L. Smarr, in Sources of Gravitational Radiation, edited by L. Smarr (Cambridge U.P., Cambridge, 1979).
4. W. Israel, Phys. Rev. 164, 1776 (1967); PHRVAO0031-899X
5. B. Carter, Phys. Rev. Lett. 26, 331 (1971); PRLTAO0031-9007