Y. A. Mitropolskiy, “Nikolai Nikolaevich Bogolyubov”, Ukr. Mat. Zhurn., vol. 44, no. 3, pp. 431–432, Apr. 1992, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/8114