Position Fair Mechanisms Allocating Indivisible Goods

Abstract

In the fair division problem for indivisible goods, mechanisms that output allocations satisfying fairness concepts, such as envy-freeness up to one good (EF1), have been extensively studied. These mechanisms usually require an arbitrary order of agents as input, which may cause some agents to feel unfair since the order affects the output allocations. In the context of the cake-cutting problem, Manabe and Okamoto (2012) introduced meta-envy-freeness to capture such kind of fairness, which guarantees the absence of envy compared to different orders of agents. In this paper, we introduce position envy-freeness and its relaxation, position envy-freeness up to $k$ goods (PEF$k$), for mechanisms in the fair division problem for indivisible goods, analogous to the meta-envy-freeness. While the round-robin or the envy-cycle mechanism is not PEF1, we propose a PEF1 mechanism that always outputs an EF1 allocation. In addition, in the case of two agents, we prove that any mechanism that always returns a maximum Nash social welfare allocation is PEF1, and propose a modified adjusted winner mechanism satisfying PEF1. We further investigate the round-robin and the envy-cycle mechanisms to measure how far they are from position envy-freeness.