V. A. Onishchuk and Y. P. . Sysak, “Local nilpotent groups satisfying a weak condition of minimality or maximality for subgroups of fixed degree of nilpotency ”, Ukr. Mat. Zhurn., vol. 44, no. 3, pp. 384–389, Apr. 1992, Accessed: Dec. 06, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/8107