1. See eg: P.S. Pershan “Structures of Liquid Crystals”, World Scientific (1988).
2. R.E. Peierls, Helv. Phys. Acta Suppl. 7: 81 (1934).
3. L.D. Landau, in “Collected Papers of L.D. Landau”, edited by D. ter Haar (Gordon and Breach, New York, 1965), 209.
4. J.M. Kosterlitz and D.J. Thouless, J. Phys. C 6: 118 (1973).
5. Very interesting related phenomena are, however, seen in helium films. See, for example, D.J. Bishop and J.D. Reppy, Phys. Rev. Lett. 40:1727 (1978).