1. W. Hanke: inFestkörperprobleme XIX, Advanced Solid State Physics (Vieweg, 1979), p. 43.
2. W. Hanke, H. J. Mattausch, andG. Strinati: inElectron Correlations in Solids, Molecules, and Atoms, edited byJ. T. Devreese andF. Brosens (Plenum Press, New York, N. Y., 1983), p. 289.
3. W. Hanke, N. Meskini, andH. Weiler: inElectronic Structure, Dynamics and Quantum Structural Properties of Condensed Matter, edited byJ. T. Devreese andP. Van Camp (Plenum Press, New York, N. Y., 1985), p. 113.
4. A. A. Abrikosov, L. P. Gorkov, andI. E. Dzyaloshinski:Methods of Quantum Field Theory in Statistical Physics (Prentice-Hall, Englewood Cliff, N.J., 1963);A. L. Fetter andJ. D. Walecka:Quantum Theory of Many-Particle Systems (McGraw-Hill, New York, N. Y., 1971);G. Rickayzen:Green’s Functions and Condensed Matter (Academic Press, London, 1980);G. D. Mahan:Many-Particle Physics (Plenum Press, New York, N. Y., 1981).
5. We follow closely the treatment due toL. Hedin andS. Lundqvist: inSolid State Physics, edited byH. Ehrenreich, F. Seitz, andD. Turnbull (Academic Press, New York, N. Y., 1969), Vol.23, p. 1, although our presentation differs from theirs in several technical details.