Kuzhel’, S. A. “On a Form of the Scattering Matrix for ρ-Perturbations of an Abstract Wave Equations”. Ukrains’kyi Matematychnyi Zhurnal 51, no. 4 (April 25, 1999): 445–457. Accessed May 26, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4630.