1. Wilson, K.G., Kogut, J.: Phys. Rep.12C, 76 (1974) Hohenberg, P.C., Halperin, B.I.: Rev. Mod. Phys.49, 435 (1977)
2. Schneider, T., Stoll, E.: Phys. Rev. B13, 1216 (1976)
3. Aharony, A.: to appear in Jour. Magnetism and Magnetic Materials
4. Halperin, B.I., Varma, C.M.: Phys. Rev. B14, 4030 (1976)
5. See articles by Müller, K.A., von Waldkirch, T., Borsa, F., Blinc, R., Rigamonti, A., In: Proceedings of the International School of Physics ?Enrico Fermi?, Course LIX 1976 on ?Local Properties at Phase Transitions? (edited by K.A. Müller and A. Rigamonti) Amsterdam: North-Holland 1976