1. F.Wegner, this Conference and references quoted there.
2. T.Lubensky, this Conference and references quoted there.
3. B.L.Altshuler, A.G.Aronov and P.A.Lee, Phys. Rev. Lett. 44, 1288 (1980).
4. R.Oppermann, this Conference.
5. See e.g. N.F.Mott, Metal Insulator Transitions, Taylor and Francis London (1974).