Kurdachenko, L.A., A.A. Pypka, and I.Ya. Subbotin. “On the Structure of Groups, Whose Subgroups Are Either Normal or Core-Free”. Reports of the National Academy of Sciences of Ukraine, no. 4 (April 28, 2019): 17–20. Accessed June 19, 2026. https://nasu-periodicals.org.ua/index.php/dp/article/view/2173.