Bazalii, B. V., and S. P. Degtyarev. “On One Boundary-Value Problem for a Strongly Degenerate Second-Order Elliptic Equation in an Angular Domain”. Ukrains’kyi Matematychnyi Zhurnal 59, no. 7 (July 25, 2007): 867–883. Accessed May 3, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3352.