Fusion of RSOS Models as a Coset Construction

Using the vertex operator approach we show that fusion of the RSOS models can be considered as a kind of coset construction which is very similar to the coset construction of minimal models in conformal field theory. We reproduce the excitation spectrum and $S$-matrix of the fusion RSOS models in the regime III and show that their correlation functions and form factors can be expressed in terms of those of the ordinary (ABF) RSOS models.