RadzievskiiG. V. “Minimality of Root Vectors of Operator Functions Analytic in an Angle”. Ukrains’kyi Matematychnyi Zhurnal 46, no. 5 (May 25, 1994): 545–566. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5718.