Kamornikov, S. F., and V. N. Tyutyanov. “On $\sigma$-Subnormal Subgroups of Finite 3’-Groups”. Ukrains’kyi Matematychnyi Zhurnal 72, no. 6 (June 17, 2020): 806-811. Accessed April 25, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/1037.