Serov, N. I., and R. M. Cherniga. “Lie Symmetries, Q-Conditional Symmetries, and Exact Solutions of Nonlinear Systems of Diffusion-Convection Equations”. Ukrains’kyi Matematychnyi Zhurnal, vol. 55, no. 10, Oct. 2003, pp. 1340-55, https://umj.imath.kiev.ua/index.php/umj/article/view/4006.