KURDACHENKO , L. A.; PYLAEV , V. V. On groups high in almost normal subgroups. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 40, n. 3, p. 326–330, 1988. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/9143. Acesso em: 17 feb. 2026.