Kuzhel’, S. A. (1999) “On a form of the scattering matrix for ρ-perturbations of an abstract wave equations”, Ukrains’kyi Matematychnyi Zhurnal, 51(4), pp. 445–457. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/4630 (Accessed: 28May2024).