Coalition-Proof Mechanisms Under Correlated Information

The paper considers two types of mechanisms that are immune from coalitional manipulations: standard mechanisms and ambiguous mechanisms. In finite-dimensional type spaces, we characterize the set of all information structures under which every efficient allocation rule is implementable via an interim coalitional incentive compatible, interim individually rational and ex-post budget-balanced standard mechanism. The requirement of coalition-proofness reduces the scope of implementability under a non-negligible set of information structures. However, when ambiguous mechanisms are allowed and agents are maxmin expected utility maximizers, coalition-proof implementation can be obtained under all most all information structures. Thus, the paper sheds light on how coalition-proofness can be achieved by engineering ambiguity in mechanism rules.