V. I. Lagno and S. V. Spichak, “Group classification of quasilinear elliptic-type equations. II. Invariance under solvable Lie algebras”, Ukr. Mat. Zhurn., vol. 63, no. 2, pp. 200–215, Feb. 2011, Accessed: Feb. 15, 2026. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/2711