Los’, V. M. “Sufficient Conditions under Which the Solutions of General Parabolic Initial-boundaryvalue problems Are Classical”. Ukrains’kyi Matematychnyi Zhurnal 68, no. 11 (November 25, 2016): 1518-1527. Accessed April 18, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/1938.