GorbachukM. L., LuchkaA. Y., MitropolskiyYu. A., and SamoilenkoA. M. “Bohdan Iosypovych Ptashnyk”. Ukrains’kyi Matematychnyi Zhurnal 49, no. 9 (September 25, 1997): 1155–1156. Accessed November 24, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5111.