NIZHNIK, L. P.; KUZHEL, S. A. Finite rank self-adjoint perturbations. Methods of Functional Analysis and Topology, [S. l.], v. 12, n. 3, p. 243–253, 2006. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/317. Acesso em: 16 dec. 2025.