  The space D(k,p) of differential operators of order at most k, from the
differential forms of degree p of a smooth manifold M into the functions of M,
is a module over the Lie algebra of vector fields of M, when it's equipped with
the natural Lie derivative. In this paper, we compute all equivariant i.e.
intertwining operators from D(k,p) into D(k',p') and conclude that the
preceding modules of differential operators are never isomorphic. We also
answer a question of P. Lecomte, who observed that the restriction to D(k,p) of
some homotopy operator, introduced in one of his works, is equivariant for
small values of k and p.
