De, G.F., Sysak, Y.P. and Franclosi, S. (1997) “On ascending and subnormal subgroups of infinite factorized groups”, Ukrains’kyi Matematychnyi Zhurnal, 49(6), pp. 842–848. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/5070 (Accessed: 5 December 2025).