SOROKOLETOVA, Olga N. Petr Petrovich Zabreiko. Journal of the Belarusian State University. Mathematics and Informatics, [S. l.], n. 1, p. 90–92, 2019. Disponível em: https://journals.bsu.by/index.php/mathematics/article/view/933. Acesso em: 18 jul. 2026.