1. Ambegaokar, V., de Gennes, P.G., and Rainer, D., 1974, Phys. Rev. A9, 2676.
2. Anderson, P.W., and Brinkman, W.F., 1973, Phys. Rev. Lett. 30, 1108.
3. Anderson, P.W., and Brinkman, W.F., 1978, in The Physics of Liquid and Solid Helium, Part II, K.H. Bennemann and J.B. Ketterson, eds., Wiley, New York, p. 177.
4. Anderson, P.W., and Morel, P., 1960, Physica 26, 671.
5. Anderson, P.W., and Morel, P., 1961, Phys. Rev. 123, 1911.