1. G. E. Volovik, JETP Lett. 31, 273 (1980).
2. E. I. Kats and V. V. Lebedev, Dynamics of Liquid Crystals [in Russian], Nauka, Moscow, 1988.
3. E. M. Aver’yanov and M. A. Osipov, Usp. Fiz. Nauk 160(5), 89 (1990); 160(10), 206 (1990) [Sov. Phys. Usp. 33, 365, 880 (1990)].
4. E. M. Aver’yanov, Zh. Éksp. Teor. Fiz. 110, 1820 (1996) [JETP 83, 1000 (1996)].
5. P. Palffy-Muhoray, V. A. Lee, and R. G. Petschek, Phys. Rev. Lett. 60, 2303 (1988).