Sevost’yanovE. A. “On the Openness and Discreteness of Mappings With Unbounded Characteristic of Quasiconformality”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 63, no. 8, Aug. 2011, pp. 1128-34, https://umj.imath.kiev.ua/index.php/umj/article/view/2789.