  Let $g$ be a reductive Lie algebra over a field of characteristic zero.
Suppose $g$ acts on a complex of vector spaces $M$ by $i_\lambda$ and
$L_\lambda$, which satisfy the identities as contraction and Lie derivative do
for smooth differential forms. Out of this data one defines cohomology of the
invariants and equivariant cohomology of $M$. We establish Koszul duality
between each other.
