Portnyahin, D. V. “Boundedness of Weak Solutions of a Nondiagonal Parabolic System of Two Equations”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 61, no. 3, Mar. 2009, pp. 400-7, https://umj.imath.kiev.ua/index.php/umj/article/view/3028.