Buhrii, O. M., & Lavrenyuk, S. P. (2001). On a Parabolic Variational Inequality That Generalizes the Equation of Polytropic Filtration. Ukrains’kyi Matematychnyi Zhurnal, 53(7), 867-878. https://umj.imath.kiev.ua/index.php/umj/article/view/4308