Y. A. Mitropolsky, N. S. Kurpel, A. Luchka, and V. N. Shevelo, “Yuri Dmitrievich Sokolov ”, Ukr. Mat. Zhurn., vol. 23, no. 2, p. 281, Feb. 1971, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/8516