Ivasyshen, S. D., & Layuk, V. V. (2011). Fundamental solutions of the Cauchy problem for some degenerate parabolic equations of the Kolmogorov type. Ukrains’kyi Matematychnyi Zhurnal, 63(11), 1469-1500. https://umj.imath.kiev.ua/index.php/umj/article/view/2819