Ivasyshen, S. D., and V. A. Litovchenko. 2010. “Cauchy Problem for a Class of Degenerate Kolmogorov-Type Parabolic Equations With Nonpositive Genus”. Ukrains’kyi Matematychnyi Zhurnal 62 (10), 1330–1350. https://umj.imath.kiev.ua/index.php/umj/article/view/2958.