  Their method was, in essence, equivalent to that of Szilard and Bennett. They considered the operation of the Szilard engine, using a device to measure and store the location of the molecule, and a correlated operation to extract heat from it. Then they reset the device. Unlike Bennett, they did not assume that resetting has a cost, and argue that this cost saves the second law. Rather, like Szilard, they imposed a modified form of the second law, and from it deduced that resetting has a cost. The generality of their claim is based upon the fact that they made no attempt to characterise the device physically, although they did assume it was capable of performing non-dissipative measurements.