1. See, for example, V. L. Ginzburg and D. A. Kirzhnits, ed., High Temperature Superconductivity. Plenum, New York, 1982, and references cited therein.
2. J. Bardeen, L. N. Cooper and J. R. Schrieffer, Phys. Rev. 108, 1175 (1957).
3. A. S. Alexandrov, J. Ranninger, and S. Robszkiewicz, Phys. Rev. Lett. 56, 949 (1986);
4. A. S. Alexandrov, J. Ranninger, and S. Robszkiewicz, Phys. Rev. B 33, 4526 (1986);
5. M.T. Beal-Monod, Phys. Rev. B 35, 8788 (1987).