Modular Invariance and Uniqueness of Conformal Characters
  We show that the conformal characters of various rational models of W-algebras can be already uniquely determined if one merely knows the central charge and the conformal dimensions. As a side result we develop several tools for studying representations of SL(2,Z) on spaces of modular functions. These methods, applied here only to certain rational conformal field theories, may be useful for the analysis of many others. 
Wolfgang Eholzer and Nils-Peter Skoruppa