1. K. von Klitzing, G. Dorda and M. Pepper, Phys. Rev. Lett. 45, 494 (1980).
2. For a review see e. g. The Quantum Hall Effect, edited by R.E. Prange and S.M. Girvin (Springer-Verlag, New York, 1987).
3. M. Buttiker in Semiconductor and Semimetals in the volume Nanostructured Systems, ed. Mark A. Reed, (Academic Press, New York, 1990).
4. F. Kuchar, in Festkörperprobleme (Advances in Solid State Physics), edited by U. Rössler (Vieweg, Braunschweig 1988), Vol. 28, p. 45.
5. J. Riess, Phys. Rev. B38, 3133 (1988).