An error in "On a new formal proof model for RFID location privacy"

In Information Processing Letters 110 (2) (2009) 57-61, Deursen and Radomirovic evaluated five formal RFID privacy models. One main result is that Ha et al.'s RFID privacy model is incorrect. The supporting fact is that a constant-response protocol cannot pass the test of Ha et al.'s RFID privacy model. However, the authors demonstrate that the constant-response protocol is artificial, and the corresponding result is therefore unwarranted. It means that Ha et al.'s RFID privacy model is not a trivial model. Hence, more effort still can be made to improve Ha et al.'s RFID privacy model.