Exponentials of Normal Operators and Commutativity of Operators: A New   Approach
  We present a new approach to the question of when the commutativity of operator exponentials implies that of the operators. This is proved in the setting of bounded normal operators on a complex Hilbert space. The proofs are based on some similarities results by Berberian and Embry as well as the celebrated Fuglede theorem. 
Mohammed Hichem Mortad
math.FA math.OA