  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}].
