Gadjiev, T. S., & Gasimova, E. R. (2008). On the smoothness of a solution of the first boundary-value problem for second-order degenerate elliptic-parabolic equations. Ukrains’kyi Matematychnyi Zhurnal, 60(6), 723–736. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/3192