Bazalii, B. V., and A. F. Tedeev. 1993. “Symmetrization and Initial Boundary-Value Problems for Certain Classes of Nonlinear Second Order Parabolic Equations”.
Ukrains’kyi Matematychnyi Zhurnal 45 (7): 884–892.
https://umj.imath.kiev.ua/index.php/umj/article/view/5880.