1. e.g. Landau, L.D., Lifschitz, E.M.: Lehrbuch der Theoretischen Physik. Vol. V: Hydrodynamik. Berlin: Akademie Verlag 1966
2. Becker, K.W., Fulde, P.: Europhys. Lett.1, 669 (1986)
3. see e.g. Forster, D.: Hydrodynamic fluctuations, broken symmetry, and correlation functions. Reading Mass: W.A. Benjamin, Inc. 1975. Here also a complete list of references can be found relating to the original work of Zwanzig, R. and Mori, H.
4. Rice, T.M., Ueda, K., Ott, H.R. Rudigier, H.: Phys. Rev. B31, 594 (1985)
5. We gratefully acknowldge discussions on this point with B. L�thi, and with C. Pethick, D. Pines and K. Quader