2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/218801A passive orthonomic system of PDEs defines a submanifold in the corresponding jet manifold, coordinated by so called parametric derivatives. We restrict the total differential operators and the prolongation of an evolutionary vector field v to this submanifold. We show that the vanishing of their commutators is equivalent to v being a generalized symmetry of the system.10 pages, no figures, unpublishedExactly Solvable and Integrable Systemstext