Liman , F. N. “Nonperiodic Groups Whose All Expanded $pd$-Subgroups Are Normal”. Ukrains’kyi Matematychnyi Zhurnal 40, no. 3 (April 28, 1988): 330–335. Accessed December 7, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/9144.