Zhernovoi, Y. V. “Conditions for One-Valued Solvability of Nonlinear Stationary Heat-Conduction Problems”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 51, no. 4, Apr. 1999, pp. 562–567, https://umj.imath.kiev.ua/index.php/umj/article/view/4641.