1. P.T. Coleridge, P. Zawadzki, A. Sachrajda: Phys. Rev. B 49, 10798 (1994)
2. L.P. Rokhinson, and V.J. Goldman, unpublished;
3. S.A.J. Wiegers, M. Specht, L.P. L??vy, M.Y. Simmons, D.A. Ritchie, A. Cavanna, B. Etienne, G. Martinez, P. Wyder: Phys. Rev. Lett. 79, 3238 (1997) for a discussion, see M.M. Fogler, and B.I. Shklovskii: Phys. Rev. B 52, 17366 (1995)
4. N. Turner, J.T. Nicholls, E.H. Linfield, K.M. Brown, G.A.C. Jones, D.A. Ritchie: Phys. Rev. B 54, 10614 (1996)
5. (a) A.A. Koulakov, M.M. Fogler, B.I. Shklovskii: Phys. Rev. Lett. 76, 499 (1996) (b) M.M. Fogler, A.A. Koulakov, B.I. Shklovskii: Phys. Rev. B 54, 1853 (1996)