Gorbachuk, M. L., A. Y. Luchka, Y. A. Mitropolskiy, and A. M. Samoilenko. “Bohdan Iosypovych Ptashnyk”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 49, no. 9, Sept. 1997, pp. 1155–1156, https://umj.imath.kiev.ua/index.php/umj/article/view/5111.