1. Schubin, S., Wonsowsky, S.: Proc. Roy. Soc. A 145, 159 (1934)
2. Schubin, S., Wonsowsky, S.: Zs. Sow. Phys. 7, 292 (1935); 10, 348 (1936)
3. Bogolyubov, N.N.: Lectures in quantum statistics. In: Selected Works, vol. 2. Naukova Dumka: Kiev (1970) [in Russian]
4. Gutzwiller, M.C.: Phys. Rev. Lett. 10, 159 (1963)
5. Hubbard, J.: Proc. Roy. Soc. A 276, 238 (1963)