1. Arnowitt, R., Deser, S., Misner, C.: Phys. Rev.118, 1100 (1960b)
2. Brill, D., Deser, S.: Ann. Phys.50, 548 (1968)
3. Hawking, S., Ellis, S.: Cambridge: Cambridge University Press 1973
4. Hoffman, D., Spruck, J.; CPAM27, 715–727 (1974)
5. Jang, P.S.: On the positivity of energy in general relativity (to be published)