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2. Seiler, R.: Remarks on the theory of particles with spin up to one in external fields. In: Troubles in the external field problem for invariant wave equations, ed. A. S. Wightman. New York: Gordon and Breach 1971
3. Hawking, S. W.: Black Holes are White Hot, Lecture given at the Seventh Texas Symposium in Relativistic Astrophysics (1974)
4. Geroch, R.: unpublished lecture notes
5. Fulling, S. A.: Scalar Quantum Field Theory in a Closed Universe of Constant Curvature, Ph. D. thesis, Princeton University (1972)