Pair-Efficient Reallocation of Indivisible Objects

We revisit the classical object reallocation problem under strict preferences. When attention is constrained to the set of Pareto-efficient rules, it is known that TTC is the only rule that is strategyproof and individually-rational. We hence relax this constraint and consider pair-efficiency. A rule is pair-efficient if it never induces an allocation at which a pair of agents gain from trading their assigned objects. Remarkably, even in the larger set of pair-efficient rules, we find that TTC is still the only rule that is strategyproof and individually-rational. Our characterization result supports the use of TTC in object reallocation problems