KOVALENKO, V. I. Locally graded groups with normal nonmetacyclic subgroups. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 59, n. 1, p. 133–135, 2007. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3296. Acesso em: 6 dec. 2025.