SEMKO, N. N. Structure of one class of groups with conditions of denseness of normality for subgroups. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 49, n. 8, p. 1148–1151, 1997. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5109. Acesso em: 5 dec. 2025.