1. R. Graham, F. Haake: Quantum Statistics in Optics and Solid State Physics, Springer Tracts in Modern Physics, Vol. 66 ( Springer, Berlin, Heidelberg 1973 )
2. H. Spohn: Rev. Mod. Phys. 53, 569 (1980)
3. F. Haake: Z. Phys. B48, 31 (1982)
4. F. Haake, R. Reibold: Phys. Rev. A32, 2462 (1985)
5. L.P. Kadanoff, G. Baym: Quantum Statistical Mechanics (Benjamin, New York 1962 )