Albeverio, S., J. F. Brasche, and V. D. Koshmanenko. “Lippmann-Schwinger Equation in the Singular Perturbation Theory”. Methods of Functional Analysis and Topology 3, no. 1 (March 25, 1997): 1–27. Accessed December 19, 2025. https://zen.imath.kiev.ua/index.php/mfat/article/view/27.