  The assumption in the main result of [Peter W. Michor: Basic Differential
Forms for Actions of Lie Groups, Proc. AMS 124, 5 (1996) 1633-1642] is removed.
Thus: A section of a Riemannian $G$-manifold $M$ is a closed submanifold $\Si$
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 $\Si$ which are invariant with respect
to the generalized Weyl group of $\Si$, without any further condition.
