SavchenkoL. I. “On the Solution Estimation of the First Boundary Value Problem for the Quasi-Linear Systems of Differential Equations of Parabolic Type ”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 23, no. 3, Apr. 1971, pp. 421-8, https://umj.imath.kiev.ua/index.php/umj/article/view/8574.