A. A. Fedotov, “Complex WKB Method (One-Dimensional Linear Problems on the Complex Plane)”, Math Notes, 114:5-6 (2023), 1418
Pseudo-Differential Operators, 14, Non-Self-Adjoint Differential Operators, Spectral Asymptotics and Random Perturbations, 2019, 135
Shafarevich A., “Quantization Conditions on Riemannian Surfaces and Spectral Series of Non-Selfadjoint Operators”, Formal and Analytic Solutions of Diff. Equations, Springer Proceedings in Mathematics & Statistics, 256, eds. Filipuk G., Lastra A., Michalik S., Springer, 2018, 177–187
A. A. Shkalikov, S. N. Tumanov, “Spectral Portraits in the Semi-Classical Approximation of the Sturm-Liouville Problem with a Complex Potential”, J. Phys.: Conf. Ser., 1141 (2018), 012155