  The fusion rule gives the dimensions of spaces of conformal blocks in the WZW
theory. We prove a dimension formula similar to the fusion rulefor spaces of
coinvariants of affine Lie algebras g^. An equivalence of filtered spaces is
established between spaces of coinvariants of two objects: highest weight
g^-modules and tensor products of finite-dimensional evaluation representations
of g\otimes\C[t].
  In the sl_2 case we prove that their associated graded spaces are isomorphic
to the spaces of coinvariants of fusion products, and that their Hilbert
polynomials are the level-restricted Kostka polynomials.
