A comment concerning cohomology and invariants of Lie algebras with   respect to contractions and deformations
  Contrary to the expected behavior, we show the existence of non-invertible deformations of Lie algebras which can generate invariants for the coadjoint representation, as well as delete cohomology with values in the trivial or adjoint module. A criterion to decide whether a given deformation is invertible or not is given in dependence of the Poincar\'e polynomial. 
R. Campoamor-Stursberg