DorogovtsevA. A., KopytkoB., KorolyukV. S., MitropolskiyY. A., SamoilenkoA. M., SytayaG. N., & SkorokhodA. V. (2002). Mykola Ivanovych Portenko (On His 60th Birthday). Ukrains’kyi Matematychnyi Zhurnal, 54(2), 147-148. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/4050