1. S. W. Lovesey,Condensed Matter Physics: dynamic correlations, Benjamin-Cummings (1986).
2. L. D. Landau,J. Phys. U.S.S.R. 5, 71 (1941).
3. R. P. Feynman,Phys. Rev. 94, 262 (1954).
4. R. P. Feynman and M. Cohen,Phys. Rev. 102, 1189 (1956).
5. A. D. B. Woods, inQuantum Fluids, edited by D. F. Brewer (North Holland Amsterdam 1965).