Intertwining operators and fusion rules for vertex operator algebras   arising from symplectic fermions
  We determine fusion rules (dimensions of the space of intertwining operators) among simple modules for the vertex operator algebra obtained as an even part of the symplectic fermionic vertex operator superalgebra. By using these fusion rules we show that the fusion algebra of this vertex operator algebra is isomorphic to the group algebra of the Klein four group over Z. 
Toshiyuki Abe, Yusuke Arike
math.QA