H. Ghazaryan and V. Margaryan, “On interior regularity of solutions of a class of almost-hypoelliptic equations. Armenian Journal of Mathematics”, Armen.J.Math., vol. 3, no. 2, pp. 32–60, Jun. 2010, Accessed: Apr. 04, 2025. [Online]. Available: https://armjmath.sci.am/index.php/ajm/article/view/71