Gorbachuk, M. L., Luchka, A. Y., Mitropolskiy, Y. A., & Samoilenko, A. M. (1997). Bohdan Iosypovych Ptashnyk. Ukrains’kyi Matematychnyi Zhurnal, 49(9), 1155–1156. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/5111