Fusion rules and the Patera-Sharp generating-function method
  We review some contributions on fusion rules that were inspired by the work of Sharp, in particular, the generating-function method for tensor-product coefficients that he developed with Patera. We also review the Kac-Walton formula, the concepts of threshold level, fusion elementary couplings, fusion generating functions and fusion bases. We try to keep the presentation elementary and exemplify each concept with the simple $\su(2)_k$ case. 
L. Begin, C. Cummins, P. Mathieu and M.A. Walton