Kuzenny , N. F., and N. N. Semko. “Structure of Periodic Metabelian Metahamiitonian Groups With an Elementary Commutant of Rank Two”. Ukrains’kyi Matematychnyi Zhurnal, vol. 40, no. 6, Nov. 1988, pp. 743-50, https://umj.imath.kiev.ua/index.php/umj/article/view/9284.