1. L. Smolin (1979), What is the problem of quantum gravity?, preprint based on part 1 of the thesis (Harvard University).
2. These questions, of course, are discussed in literature. Some good reviews of quantum gravity are by C. J. Isham, in Quantum Gravity I & II (eds. C. J. Isham, R. Penrose and D. W. Sciama; C.U.P., 1975,1980); J. A. Wheeler in Relativity, Groups and Topology (eds. B. S. De Witt and C. De Witt; Gordon and Breach, 1964); J. Hartle in The Very Early Universe (eds. G. W. Gibbons, S. W. Hawking, S. T. C. Silkos; Cambridge, 1983) and the various articles in Quantum Theory of Gravity (ed. S. Christensen, Adam Hilger, 1984).
3. E.g. G.’ t Hooft (1973), Nucl. Phys. B62, 444; S. Deser and P. Van Nieuwenhuizen (1974), Phys. Rev. D10, 401, 411.
4. T. Padmanabhan, T. R. Seshadri and T. P. Singh (1985) J. Mod. Phys. (to appear);
5. K. Eppeley and E. Hannah (1977), Found. Phys. 7, 51; D. N. Page and C. D. Geilker (1981), Phys. Rev. Letts. 47, 979.