  For Penrose and Bennett's resolution to succeed, it is necessary that the demon be conceived of as a particular type of physical system, as the physical constitution of the demon's memory must now be taken into account. If the demon is presumed to be representable by a Hamiltonian system, then it has been reduced to a mechanical device, not too dissimilar to Smoluchowski's trapdoor and spring. It is not so surprising that being a Hamiltonian system, and subject to Liouville's Theorem, might naturally lay some physical constraint upon a demon, rendering it tamable. However, the existence and exact nature of this constraint, and the possibility of a corresponding modified second law, remains open to debate and depends in a large measure on the approach taken to understanding statistical mechanics.