1. A detailed summary on proximity effects in superconductivity is given by G. Deutscher and P. G. de Gennes. In: Superconductivity. Ed.: R. D. Parks. New York: Marcel Dekker, Inc. 1969.
2. Krätzig, E., Walther, K., Schilz, W.: Phys. Letters30 A, 411 (1969).
3. Krätzig, E.: Phys. Letters33 A, 343 (1970) and
4. Krätzig, E.: Solid State Commun.9, 1205 (1971).
5. Orsay Group on Superconductivity. In: Quantum Fluids, Proc. of the 1965 Sussex University Symposium. Ed.: D. Brewer. Amsterdam: North Holland Publ. Co. 1966.