1. 1) For example, M. Born and K. Huang: Dynamical Theory of Crystal Lattices, Oxford University Press, Oxford, (1954).
2. 2) T. Matsubara: J. Phy. Soc. Japan, 7 (1952), 270.
3. 3) H. Kanzaki: J. Phys. Soc. Japan, 7 (1952), 270.
4. 4) M. A. Krivoglaz and E. A. Tikhonova: Ukr. Fig., Zh., 3 (1958), 297.
5. 5) A. G. Khachaturyan: Soviet Phys. Solid St., 4 (1963), 2081.