PLOTKIN, Ya. D.; TURBIN, A. F. Reversion of linear operators disturbed on the spectrum . Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 23, n. 2, p. 168–176, 1971. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8499. Acesso em: 6 dec. 2025.