1. D.R. Tilley, G.J. van Gurp, C.W. Berghout, Phys.Lett. 12, 305 (1964)
2. W.A. Reed, E. Fawcett, P.P.M. Meincke, P.C. Hohenberg, N.R. Werthamer, Proc.LT10, Moscow, (Ed.M.P. Malkov), Viniti 1967, Vol. IIA, p. 368
3. P.C. Hohenberg, N.R. Werthamer, Phys.Rev. 153, 493 (1967)
4. K. Takanaka, T. Nagashima, Progr.Theor.Phys. 43, 18 (1970)
5. K.D. Harms, Z.Naturforsch. 25a, 1161 (1970)