Pines, D., Nozières, P.: The Theory of Quantum Liquids, I. New York-Amsterdam: W. A. Benjamin 1966.
March, N. H.: In: Mathematical Methods in Solid State and Superfluid Theory. Scottish Universities' Summer School 1967. Eds.: R. C. Clark and G. H. Derrick, Edinburg: Oliver & Boyd 1969.
Morita, T.: Progr. theor. Phys., Suppl.44, 69 (1969).
London, F.: Superfluids, II. New York: J. Wiley and Sons 1954.
Kubo, R.: Statistical Mechanics. Amsterdam: North Holland 1965.