Tushev, A. V. “On Solvable Groups With Proper Quotient Groups of Finite Rank”. Ukrains’kyi Matematychnyi Zhurnal 54, no. 11 (November 25, 2002): 1560–1568. Accessed April 7, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/4192.