CHEREMNIKH, E. V. On normal eigenvalue imbedded in continuous spectrum. Methods of Functional Analysis and Topology, [S. l.], v. 7, n. 1, p. 1–16, 2001. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/134. Acesso em: 17 dec. 2025.