RADZIEVSKY, G. V. Multiple minimality of the root vectors of polynomial operators bunch, perturbed by analytical operator-function $S (\lambda)$ с $S (\infty) = 0$ outside the circle . Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 40, n. 5, p. 599–610, 1988. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8808. Acesso em: 6 dec. 2025.