Andreeva, N. V., N. I. Serov, and L. O. Tulupova. 2000. “$Q$-Conditional Symmetry of a Nonlinear Two-Dimensional Heat-Conduction Equation”. Ukrains’kyi Matematychnyi Zhurnal 52 (6), 846-49. https://umj.imath.kiev.ua/index.php/umj/article/view/4481.