RadzievskyG. V. (1988). 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, 40(5), 599-610. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/8808