KOPYTKO, B. I.; OSYPCHUK, M. M. Mykola Ivanovych Portenko (on his 80th birthday) . Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 75, n. 11, p. 1446–1449, 2023. DOI: 10.3842/umzh.v75i11.7250. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/7250. Acesso em: 5 dec. 2025.