On the classification of admissible representations of the virasoro algebra

For the Virasoro algebra, the problems of classifying bounded admissible re presentations, on the one hand, and finite-length extensions of highest wei ght modules, on the other hand, are wild: they are as complicated as the pr oblem of classifying a pair of matrices. This follows from results by Marti n and Piard and Feigin and Fuchs.