DOROGOVTSEV, A. A.; KOPYTKO, B.I.; OSIPCHUK, M. M. Mykola Ivanovych Portenko (on his 75th birthday). Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 69, n. 12, p. 1714–1716, 2017. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/1814. Acesso em: 5 dec. 2025.