1. P.C. Martin in Superconductivity ed. R.D (1970). Parks.
2. R.V. Carlson and A.M. Goldman, Phys. Rev. Lett.3411 (1975).
3. P.W. Anderson, Phys. Rev. 112 1900 (1958).
4. D. A. Bonn et al, Phys. Rev. B 35 R8843 (1987).
5. B. Koch, M. Dueler, H.P. Geserich, Th. Wolf, G. Roth, and G. Zachman, in Electronic Porperties of High- Tc Superconductors, ed. by H. Kuzmany, M. Mehring and J. Fink, Springer 1990.