Chernikov, S. N. “Investigations of O. Yu Shmidt in the Theory of Infinite Groups”. Ukrains’kyi Matematychnyi Zhurnal 23, no. 5 (September 3, 1971): 591–597. Accessed April 7, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/8331.