2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/123203We consider the problem of performing the preliminary "symmetry classification'' of a class of quasi-linear PDE's containing one or more arbitrary functions: we provide an easy condition involving these functions in order that nontrivial Lie point symmetries be admitted, and a "geometrical'' characterization of the relevant system of equations determining these symmetries. Two detailed examples will elucidate the idea and the procedure: the first one concerns a nonlinear Laplace-type equation, the second a generalization of an equation (the Grad-Schlüter-Shafranov equation) which is used in magnetohydrodynamics.15 pages; to be published in Nonlinear DynamicsMathematical Physics22E70;35Q35text