Bakhtin, A. K., L. Vyhovs’ka, and I. V. Denega. “Inequalities for Inner Radii of Symmetric disjoint domains”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 70, no. 9, Sept. 2018, pp. 1282-8, http://umj.imath.kiev.ua/index.php/umj/article/view/1634.