1. P. W. Anderson, in: Proceedings VII International Conference on Low Temperature Physics, Toronto, 1960, Univ. of Toronto Press, 1961, p. 298.
2. I. Giaever, Ibid,p. 327.
3. I. Giaever, H. R. Hart, and K. Megerle, Phys. Rev. 126: 941 (1962).
4. P. Morel and P. W. Anderson, Phys. Rev. 125: 1263 (1962).
5. J. C. Swihart, IBM J. Res. Develop. 6: 14 (1962).