1. See, for example, J. C. Wheatley, Progress in Low Temperature Physics, Vol. VI, C.J. Gorter, ed. (North-Holland, Amsterdam, 1970) Ch. 3.
2. A. F. Andreev, Zh. Eskp. Teor. Fiz. 50, 1415 (1966) [Sov Phys.-JETP 23, 939 (1966)].
3. D. O. Edwards and W. F. Saam, in Progress in Low Temperature Physics, D. F. Brewer, ed. (North-Holland, Amsterdam, 1978), Vol. 7A, Ch.4, p.283.
4. J. L. Epstein and E. Krotscheck, Phys. Rev. B 37, 1666 (1988).
5. N. Pavloff and J. Treiner, J. Low Temp. Phys. 83, 15 (1991).