Kuzhel’S. A. “On Elements of the Lax-Phillips Scattering Scheme for $ρ$-Perturbations of an Abstract Wave Equation”. Ukrains’kyi Matematychnyi Zhurnal 50, no. 12 (December 25, 1998): 1615–1629. Accessed July 27, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/4781.