KUZHEL', S. A. On a form of the scattering matrix for ρ-perturbations of an abstract wave equations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 51, n. 4, p. 445–457, 1999. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4630. Acesso em: 6 dec. 2025.