1. Proc. of the NATO Advanced Study Institute on Gravitation: recent developments;Parker,1979
2. General relativity and gravitation;Davies,1980
3. General relativity: an Einstein centenary survey;Gibbons,1979
4. The validity of the semi-classical approximation is discussed in, for example, M. Duff, Inconsistency of quantum field theory in curved space-time, in: Proc. Second Oxford Quantum gravity Conf., to be published
5. In-out semi-classical gravity and quantum gravity