2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/159354This article reviews the use of differential forms and Lie derivatives to find symmetries of differential equations, as originally presented by Harrison and Estabrook, J. Math. Phys., 12 (1971), 653. An outline of the method is given, followed by examples and references to recent papers using the method.Published in SIGMA (Symmetry, Integrability and Geometry: Methods and Applications) at http://www.emis.de/journals/SIGMA/Mathematical PhysicsExactly Solvable and Integrable Systems22E70; 34A26; 35A25; 35A30; 53Z05text