POLOVITSKII, Ya. D. Some obligatory conditions and generalizations of the Fedorov theorem. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 49, n. 4, p. 566–572, 1997. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5032. Acesso em: 14 apr. 2025.