1. For the discussion of S
GH see: Gibbons, G. W., and Hawking, S. W.: 1977, Phys. Rev. D15, 2738.
2. Hawking, S. W.: 1979, in General Relativity — An Einstein Centenary Survey (eds S. W. Hawking and W. Israel), Cambridge.
3. For the discussion of the boundary value problem in geometrodynamics, see: Isenberg J., and Wheeler, J. A.: 1979 in Relativity, Quanta and Cosmology (eds M. Pantaleo and F. De Finis), Johnson, New York, p. 267.
4. A discussion of Green’s functions and their inverses will be found in: Morse, P. M., and Feschbach, H.: 1953, Methods of Mathematical physics, McGraw-Hill, New York.
5. DeWitt, B. S., and Brehme, R. W.: 1960, Ann. Phys. 9, 220.