Chernikov , S. N., and S. S. Levishchenko. “Constructive Description of Finite Nondispersed Groups Where All Subgroups of the Nonprimary Index Are Abelian ”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 44, no. 6, July 1992, pp. 818-22, https://umj.imath.kiev.ua/index.php/umj/article/view/8015.