A Global version of Grozman's theorem
  Let X be a manifold. The classification of all equivariant bilinear maps between tensor density modules over X has been investigated by Yu Grozman, who has provided a full classification for those which are differential operators. Here, we investigate the same question without the hypothesis that the maps are differential operators. In our paper, the geometric context is algebraic geometry and the manifold X is the circle Spec C[z,z^{-1}]. 
Kenji Iohara and Olivier Mathieu
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