QUANTUM GROUPS AND FUSION RULES MULTIPLICITIES

We perform explicitly a truncation of the tensor product of two regular representations of Uq(g) for q a root of unity and show that it coincides with the fusion rules for integrable representations in a WZW theory based on the affine Lie algebra g(1). We obtain a new formula for the multiplicities which may be useful in practical calculations and which generalizes a classical formula of Weyl. © 1990.