LAHNO, V. I.; SPICHAK, S. V. Group classification of quasilinear elliptic-type equations. I. Invariance with respect to Lie algebras with nontrivial Levi decomposition. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 59, n. 11, p. 1532–1545, 2007. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3409. Acesso em: 6 dec. 2025.