Olshansky , A. Yu. “Nesting of Periodical Groups into Simple Periodica Groups”. Ukrains’kyi Matematychnyi Zhurnal 44, no. 6 (July 7, 1992): 845–847. Accessed February 17, 2026. https://umj.imath.kiev.ua/index.php/umj/article/view/8021.