1. Boccara, N. (ed.), Symmetries and Broken Symmetries in Condensed Matter Physics. IDSET Paris, 1981
2. Dzyaloshinskii, I., in Symmetries and Broken Symmetries in Condensed Matter Physics, ed. N. Boccara. IDSET, Paris, 1981, p. 29
3. Landau, L. D. and Lifshitz, E. M., Statistical Physics. Addison-Wesley, Reading, Massachusetts, 1958
4. Anderson, P. W., in Symmetries and Broken Symmetries in Condensed Matter Physics, ed. N. Boccara. IDSET, Paris, 1981, p. 11