Dorogovtsev, A. A., B.I. Kopytko, and M. M. Osipchuk. “Mykola Ivanovych Portenko (on His 75th Birthday)”. Ukrains’kyi Matematychnyi Zhurnal 69, no. 12 (December 25, 2017): 1714–1716. Accessed December 5, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/1814.