Polovitskii, Ya. D., N. S. Chernikov, and V. L. Chechulin. 1996. “Groups With Incidence Condition for Noncyclic Subgroups”. Ukrains’kyi Matematychnyi Zhurnal 48 (4), 533-39. https://umj.imath.kiev.ua/index.php/umj/article/view/5316.