On special covariants in the exterior algebra of a simple Lie algebra
  We study the subspace of the exterior algebra of a simple complex Lie algebra linearly spanned by the copies of the little adjoint representation or, in the case of the Lie algebra of traceless matrices, by the copies of the n-th symmetric power of the defining representation. As main result we prove that this subspace is a free module over the subalgebra of the exterior algebra generated by all primitive invariants except the one of highest degree. 
Corrado De Concini, Pierluigi M\"oseneder Frajria, Paolo Papi and   Claudio Procesi
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