1. J. Alev, T.J. Hodges, J.-D. Velez, Fixed rings of the Weyl algebra A
1
(ℂ), J. Alg., 130, 1990, 83–96.
2. J.L. Brylinski, A differential complex for Poisson manifolds, J. Diff. Geom., 28, 1988, 93–114.
3. H. Cartan & S. Eilenberg, Homological algebra, Princeton University Press, 1956.
4. L. Chiang, H. Chu, M. Kang, Generation of Invariants, preprint.
5. Bull. Soc. Math. France;J Dixmier,1968