Vincenzi, G., L. A. Kurdachenko, and A. Russo. “On Some Groups All Subgroups of Which Are Nearly Pronormal”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 59, no. 10, Oct. 2007, pp. 1331–1338, https://umj.imath.kiev.ua/index.php/umj/article/view/3392.