Kitaybekov, E. T. “Solvability Dirichlet Problem for Three-Dimensional Elliptic-Parabolic Equations With Type and Order Extinction”. Journal of Mathematics, Mechanics and Computer Science, vol. 92, no. 4, July 2018, pp. 40-45, https://bm.kaznu.kz/index.php/kaznu/article/view/452.