Double Implementation in Dominant Strategy Equilibria and Ex-Post Equilibria with Private Values

Abstract We consider the implementation problem for incomplete information and private values. We investigate double implementability of social choice functions in dominant strategy equilibria and ex-post equilibria. We define a new strategic axiom that implies “strategy-proofness” and that is implied by “secure strategy-proofness,” but the converse of these relationships does not hold. We call it “weak secure-strategy-proofness.” We show that a social choice function is doubly implementable if and only if it is weakly securely-strategy-proof.