A Generalized Rule For Non-Commuting Operators in Extended Phase Space
  A generalized quantum distribution function is introduced. The corresponding ordering rule for non-commuting operators is given in terms of a single parameter. The origin of this parameter is in the extended canonical transformations that guarantees the equivalence of different distribution functions obtained by assuming appropriate values for this parameter. 
S. Nasiri, S. Khademi, S. Bahrami, and F. Taati