 The supertask underpinning this model requires an infinite number of interactions. As Hepp and Bell described it, the model was unrealistic because it required an infinite amount of time. However, a similar system was shown by Wan (1980) and Bub (1988) to take place in finite time. Their approach appears at first glance to be a promising model of measurement. However, Landsman (1991) pointed out that it is inadequate on one of two levels: either the dynamics is not automorphic (which is the analogue of unitarity for such systems), or the task is not completed in finite time. Landsman (1995) has argued that neither of these two outcomes is plausible for a realistic local description of a quantum system.