1. I. L. Landau and Yu. V. Sharvin,JETP Lett. 10, 121 (1969).
2. D. Robin, F. Rothen, and L. Rinderer,Helv. Phys. Acta 49, 697 (1976).
3. L. D. Landau, private communication to D. Shoenberg; see D. Shoenberg,Superconductivity (Cambridge University Press, 1938), p. 59.
4. A. F. Andreev and P. Tekel,Sov. Phys.?JETP 35, 807 (1972).
5. L. P. Gorkov and O. N. Dorokhov,Sov. Phys.?JETP 40, 956 (1974).