1. For recent reviews, see S. Hunklinger and A.K. Raychaudhury: Progr. Low Temp. Physics, ed. by D.F. Brewer, vol. 9 (Elsevier — North Holland, Amsterdan 1985) p. 265
2. R.O. Pohl, Phase Transitions 5, 239 (1985)
3. P.W. Anderson, B.I. Halperin and C.M. Varma: Philos. Mag. 25, 1 (1972)
4. W.A. Phillips: J. Low. Temp. Phys. 7, 351 (1972)
5. R.O. Pohl, W.F. Love and R.B. Stephens: In Amorphous and Liquid Semiconductors, ed. by J. Stuke and W. Brenig (Taylor and Francis 1974) p.1121