Revisiting the displacement operator for quantum systems with   position-dependent mass
  Recently R. N. Costa Filho et al. (PRA 84, 050102(R) (2011)) have introduced a position dependent infinitesimal translation operator which corresponds to a position dependent linear momentum and consequently to a position dependent effective mass quantum particle. Although there is no doubt in novelty of the idea and the formalism, we believe that some aspects of the quantum mechanics could be complemented in their original work. Here in this letter first we address those points and then an alternative will be introduced. Finally we apply the formalism for a quantum particle under a null potential confined in a square well and the results will be compared with those in the paper mentioned above. 
S. Habib Mazharimousavi
quant-ph