A demon has a large number of boxes with a single particle in. He / she adiabatically introduces a wall in the box, dividing it in two with a particle in one of the two halves (L, R). The demon does not measure which half the particle is in (and so doesn't have to store any bits of information). With a large collection of Szilard engines prepared in this way, the demon pairs them up. Half the time, the particle will be in the same side, and half the time they will be anti-correlated. He connects the movable walls in the two boxes by a piston that has a ribbon on it, and allows the boxes to adiabatically expand. If the ribbon moves, then the particles are in the same side (though we dont know if L or R), and if the ribbon doesn't move they are anti-correlated. Therefore by post-selection, the demon can prepare anti-correlated pairs of Szilard engines. Is this possible? And if so, does measuring the ribbon (correlated, anti-correlated) require the demon to store a bit of information? If so, this will still be more energetically favourable than simply compressing the two boxes to prepare the anti-correlated Szilard engines (which, i think is because in that case we know exactly where the atoms are). Thanks!