Malyts’ka, H. P. “On the Maximum Principle for Ultraparabolic Equations”. Ukrains’kyi Matematychnyi Zhurnal 48, no. 2 (February 25, 1996): 195–201. Accessed April 11, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/5347.