Kovaleva, V. A. “Finite Groups With Given Systems of $K-\mathfrak{U}$-Subnormal Subgroups”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 68, no. 1, Jan. 2016, pp. 52-63, https://umj.imath.kiev.ua/index.php/umj/article/view/1821.