1. H. de Vries, Acta Crystallogr. 4, 219 (1951).
2. E. I. Kats, Zh. Éksp. Teor. Fiz. 59, 1854 (1970) [Sov. Phys. JETP 32, 1004 (1971)].
3. V. N. Belyi and A. N. Serdyukov, Dokl. Akad. Nauk BSSR 18, 402 (1974).
4. V. A. Belyakov, Diffraction Optics of Periodic Media with Complex Structure (Nauka, Moscow, 1988).
5. S. Chandrasekhar, Liquid Crystals (Cambridge University Press, Cambridge, 1977; Mir, Moscow, 1980).