Heisenberg duoble, pentagon equation, structure and classification of   finite dimensional Hopf algebras
  The study of the pentagon (fusion) equation leds to the Structure and the Classification theorem for finite dimenasional Hopf algebras: there exists a one to one correspondence between the set of types of n-dimensional Hopf algebtras and the set of the orbits of the resticted Jordan action $GL_n(k) \times M_n(k)\otimes M_n(k) \to M_n(k) \otimes M_nk$ $(u, R) \to (u\otimes u)R (u\otimes u)^{-1}$, the representatives of wich are invertible solutions of length n of the pentagon equation. 
G. Militaru