1. D. Shechtman, L Blech, D. Gratias, and J.W. Cahn, Phys. Rev. Lett. 53, 1951 (1984).
2. 1. L.D. Landau and E.M. Lifshitz, Statistical Physics, Pergamon, London, 1969, Chap. 14
3. 2. L.D. Landau, in Collected Papers of L.D. Landau, edited D. ter Haar, Gordon and Breach Pergamon, New York, 1965, p. 193.
4. C.L. Henley, Comm. Cond. Matt. Phys. 13, 59 (1987).
5. D. Gratias, Contemp. Phys. 28, 219 (1987).