Efficient Coalition-Proof Full Implementation
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Abstract
D'Apresmont Gerard-Varet (AGV) mechanism implements efficient social choice in a budget-balanced manner, however it is susceptible to a joint misreport by a coalition of agents, and it may have inefficient equilibria. This paper extends AGV mechanism by putting more structure on its monetary transfers; in the resulting direct mechanism each agent is paid the Shapley value generated from the expected externalities his report imposes on others. This makes each group of agents to be paid in total the expected externality their report imposes on others, and makes it Bayesian incentive compatible to report truthfully. Moreover, any agent can guarantee to receive his ex ante efficient payoff by reporting truthfully, making all equilibria efficient. It is generically impossible to make truthful report a dominant strategy for all coalitions.