1. M. Dimassi, “Spectral Shift Function and Resonances for Slowly Varying Perturbations of Periodic Schrödinger Operators,” J. Funct. Anal. 225(1), 193–228 (2005).
2. L. Faddeev and V. Zakharov, “Korteveg-de Vries Equation: a Completely Integrable Hamiltonian System,” Funct. Anal. Appl. 5, 18–27 (1971).
3. N. Firsova, “Resonances of the Perturbed Hill Operator with Exponentially Decreasing Extrinsic Potential,” Mat. Zametki 36, 711–724 (1984).
4. N. Firsova, “A Direct and Inverse Scattering Problem for a One-Dimensional Perturbed Hill Operator,” Mat. Sb. 130(172) (3), 349–385 (1986).
5. N. Firsova, “Levinson Formula for Perturbed Hill Operator,” Teoret. Mat. Fiz. 62(2), 196–209 (1985).