STRATEGY-PROOF COALITION FORMATION *

We analyze coalition formation problems in which a group of agents is partitioned into coalitions and agents ' preferences only depend on the coalition they belong to. We study rules that associate to each profile of agents ' preferences a partition of the society. We focus on strategy-proof rules on restricted domains of preferences, as the domains of additively representable or separable preferences. In such domains, only single-lapping rules satisfy strategy-proofness, individual rationality, non-bossiness, and flexibility. Single-lapping rules are characterized by severe restrictions on the set of feasible coalitions. These restrictions are consistent with hierarchical organizations and imply that single-lapping rules always select core-stable partitions. Thus, our results highlight the relation between the non-cooperative concept of strategy-proofness and the cooperative concept of core-stability. We analyze the implications of our results for matching problems * Acknowledgements: I want to express my gratitude for their hospitality to the W.A. Walli