IgnatenkoV. F. “Diametral Theory of Algebraic Surfaces and Geometric Theory of Invariants of Groups Generated by Reflections. II”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 50, no. 6, June 1998, pp. 792–802, https://umj.imath.kiev.ua/index.php/umj/article/view/4889.