Skrypnik, I. I. “A Necessary Condition for the Regularity of a Boundary Point for Degenerating Parabolic Equations With Measurable Coefficients”. Ukrains’kyi Matematychnyi Zhurnal 56, no. 6 (June 25, 2004): 818–836. Accessed May 5, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3801.