1. L. G. Brown, ``Lidskii's theorem in the type II case'' in Geometric Methods in Operator Algebras (Kyoto, 1983), ed. H. Araki and E. G. Effros, Pitman Res. Notes Math. Ser. 123, Longman Sci. Tech., Harlow, 1986, 1--35.
2. A. Ya. Gordon, On the point spectrum of the one-dimensional Schrödinger operator (in Russian), Uspekhi Mat. Nauk 31 (1976), no. 4, 257--258.
3. U. Haagerup and M. Rørdam, Perturbations of the rotation $C^*$-algebras and of the Heisenberg commutation relation, Duke Math. J. 77 (1995), 627--656.
4. R. Mañé, Ergodic Theory and Differentiable Dynamics, Ergeb. Math. Grenzgeb. (3) 8, Springer-Verlag, Berlin, 1987.
5. M. Reed and B. Simon, Methods of Modern Mathematical Physics, IV: Analysis of Operators, Academic Press, New York, 1978.