I. V. Ostrovskii, “M. G. Krein’s investigations in the theory of entire and meromorphic functions and their further development”, Ukr. Mat. Zhurn., vol. 46, no. 1-2, pp. 87–99, Feb. 1994, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/5772