KUZHEL', S. A.; VAVRYKOVYCH, L. On infinite-rank singular perturbations of the Schrödinger operator. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 60, n. 4, p. 487–496, 2008. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3171. Acesso em: 14 apr. 2025.