Bondarenko, V. G., and Yu. Yu. Prokopenko. “Barrier Functions for One Class of Semilinear Parabolic Equations”. Ukrains’kyi Matematychnyi Zhurnal 60, no. 11 (November 25, 2008): 1449–1456. Accessed April 19, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3260.