SerovN. I. and ChernigaR. M., “Lie Symmetries, <em class="a-plus-plus">Q</em&gt;-Conditional Symmetries, and Exact Solutions of Nonlinear Systems of Diffusion-Convection Equations”, Ukr. Mat. Zhurn., vol. 55, no. 10, pp. 1340-1355, Oct. 2003.