1. H.A. Kastrup, Phys. Lett. B 413 (1997) 267; to the list of quoted authors discussing the spectrum (1) the following should be added: T. Brotz, C. Kiefer, Phys. Rev. D 55 (1997) 2186.
2. S.W. Hawking, in: S.W. Hawking, W. Israel (Eds.), General Relativity, an Einstein centenary survey, Cambridge University Press, Cambridge etc., 1979, ch. 15; (reprinted, in: G.W. Gibbons, S.W. Hawking (Eds.), Euclidean Quantum Gravity, World Scientific, Singapore etc., 1993, p. 29; this book contains reprints of the Refs. [4], [13], [20] and [23] of the present paper, too).
3. J.S. Langer, Ann. Physics 41 (1967) 108; 54 (1969) 258; Physica 73 (1974) 61; in: L. Garrido (Ed.), Systems Far from Equilibrium (Lecture Notes in Physics 132), Springer-Verlag, Berlin etc., 1980, p. 12.
4. D.J. Gross, M.J. Perry, L.G. Yaffe, Phys. Rev. D 25 (1982) 330.
5. I thank H. Müller-Krumbhaar, D. Stauffer for corresponding private communications.