Romanenko, I. B., and I. V. Skrypnik. “A Priori Estimates of Solutions of Linear Parabolic Problems With Coefficients from Sobolev Spaces”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 51, no. 11, Nov. 1999, pp. 1534–1548, https://umj.imath.kiev.ua/index.php/umj/article/view/4755.