M. Y. Dudkin, “Analog of the Krein Formula for Resolvents of Normal Extensions of a Prenormal Operator”, Ukr. Mat. Zhurn., vol. 54, no. 4, pp. 555–562, Apr. 2002, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/4092