LagnoV. I., and SpichakS. V. “Group Classification of Quasilinear Elliptic-Type Equations. II. Invariance under Solvable Lie Algebras”. Ukrains’kyi Matematychnyi Zhurnal 63, no. 2 (February 25, 2011): 200-215. Accessed November 23, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2711.