1. see, e.g., J.G. Dash, Phase transitions at interfaces: Roughening, surface melting and triple point wetting, Solvay Conference on Surface Science (University of Texas, 1987 )
2. H.J. Lauter, Inelastic neutron scattering from adsorbates, Phonons 89, eds. S.Hunklinger, W. Ludwig and G.Weiss (World scientific, 1990), p.871, and contribution at this conference
3. M.W. Cole, Rev. Mod. Phys. 46, 451 (1974)
4. C.C. Grimes, Surf. Sci. 73, 379 (1978)
5. V.S. Edelman, Sov. Phys. Usp.23, 227 (1980)