Piskun, M.M. and Semko, N.N. (2009) “On some generalizations of nearly normal subgroups”, Ukrains’kyi Matematychnyi Zhurnal, 61(10), pp. 1381–1395. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/3108 (Accessed: 14 April 2025).