Bondar , A.V. and Romanenko , V.Y. (1991) “Some conditions of holomorphism in the Hilbert spaces”, Ukrains’kyi Matematychnyi Zhurnal, 43(1), pp. 35–40. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/9302 (Accessed: 6 December 2025).