1. V. N. Bogomolov, Phys. Rev. B 51, 17040 (1995).
2. S. Yu. Krylov, A. V. Prosyanov, and J. J. M. Beenakker, J. Chem. Phys. 107, 6970 (1997).
3. J. J. M. Beenakker, V. D. Borman, and S. Yu. Krylov, Phys. Rev. Lett. 103, 4622 (1994).
4. Yu. N. Devyatko and V. N. Tronin, Zh. Éksp. Teor. Fiz. 98, 1570 (1990) [Sov. Phys. JETP 71, 880 (1990)].
5. V. D. Borman, S. Yu. Krylov, and A. V. Prosyanov, Zh. Éksp. Teor. Fiz. 97, 1795 (1990) [Sov. Phys. JETP 70, 1013 (1990)].