2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/151998A section of a Riemannian $G$-manifold $M$ is a closed submanifold $Σ$ which meets each orbit orthogonally. It is shown that the algebra of $G$-invariant differential forms on $M$ which are horizontal in the sense that they kill every vector which is tangent to some orbit, is isomorphic to the algebra of those differential forms on $Σ$ which are invariant with respect to the generalized Weyl group of this orbit, under some condition.10 pages, ESI Preprint 87, AmSTeXDifferential Geometrytext