KURDACHENKO, L. .; PYPKA, A. .; SUBBOTIN, I. . On groups, whose non-normal subgroups are either contranormal or core-free . Reports of the National Academy of Sciences of Ukraine, Kyiv, Ukraine, n. 10, p. 3–8, 2020. DOI: 10.15407/dopovidi2020.10.003. Disponível em: https://nasu-periodicals.org.ua/index.php/dp/article/view/2020-10-1. Acesso em: 29 may. 2026.