Ex Post Implementation

We analyze the problem of fully implementing a social choice set in ex post equilibrium. Weidentify an ex post monotonicity condition that is necessary and -- in economic environments -- sufficient for full implementation in ex post equilibrium. We also identify an ex post monotonicityno veto condition that is sufficient. Ex post monotonicity is satisfied in all single crossing environments with strict ex post incentive constraints. In many economically significant environments, ex post implementation can be achieved in the direct mechanism. We show by means of two classic examples that ex post monotonicity does not imply nor is it implied by Maskin monotonicity (necessary and almost sufficient for complete information implementation). The single unit auction with interdependent valuations is shown to satisfy ex post monotonicity but not Maskin monotonicity. Ex post implementation in the direct mechanism is also possible in this case. We describe an example where the Pareto correspondence fails ex post monotonicity but Maskin monotonicity is satisfied.Ex post equilibrium, Implementation, Single crossing, Interdependent values

Nuclear Weapons and National Prestige

Leaders and historians see prestige as important, but international relations theorists have neglected the concept, in part for lack of a clear definition. It is proposed that a party "holds prestige" when group members generally believe that the party has a certain desirable quality, and this situation gives the party perceived power in the group. The definition gains support from a survey of international affairs writings on the sources of prestige. Prestige is strategically important when a party wants support from others who would rather join the side that more of the others are joining. Some general ways of acquiring prestige are discussed. Compared to achieving social progress, building and testing nuclear weapons is better at bearing prestige because it has distinct borders separating success and failure, because it is salient and because it involves the symbolism of power. In some cases when prestige is a factor, one can better demonstrate one’s ability to perform an accomplishment by refraining from doing it. The analysis yields suggestions for reducing nuclear proliferation.prestige, nuclear weapons, common knowledge, signaling, countersignaling, global games, symbolism

Vickrey Auctions with Reserve Pricing

We generalize the Vickrey auction to allow for reserve pricing in a multiple item auction with interdependent values. By withholding quantity in some circumstances, the seller can improve revenues or mitigate collusion. In the Vickrey auction with reserve pricing, the seller determines the quantity to be made available as a function of the bidders' private information, and then efficiently allocates this quantity among the bidders. Truthful bidding is a dominant strategy with private values and an ex post equilibrium with interdependent values. If the auction is followed by resale, then truthful bidding remains an equilibrium in the auction-plus-resale game. In settings where resale exhausts all the gains from trade among the bidders, the Vickrey auction with reserve pricing maximizes seller revenues.Auctions, Vickrey Auctions, Multiple Item Auctions, Resale

Multi-Unit Open Ascending Price Efficient Auction

This paper presents an open ascending price mechanism that allocates efficiently M units of the same good among N bidders with interdependent values The mechanism consists of a number of sequential English auctions with reentry and has the following attributes. In each of the individual auctions all the bidders compete simultaneously in the open ascending price format. The most distinctive feature of the mechanism is that winners are determined first, and then additional auxillary auctions are conducted to determine prices. The total number of auctions depends only on the number of goods to be allocated and not on the number of bidders.Multiple units, Interdependent values, Sequential auctions, Ascending price auction

Robust Implementation: The Case of Direct Mechanisms"

A social choice function is robustly implementable if there is a mechanism under which the process of iteratively eliminating strictly dominated messages leads to outcomes that agree with the social choice at every type profile. In an interdependent value environment with single crossing preferences, we identify a strict contraction property on the preferences which together with strict ex post incentive compatibility is sufficient to guarantee robust implementation in the direct mechanism. Strict EPIC and the contraction property are also necessary for robust implementation in any mechanism. The contraction property essentially requires that the interdependence is not too large. In a linear signal model, the contraction property is equivalent to an interdependence matrix having an eigenvalue less than one.Mechanism design, Implementation, Robustness, Common knowledge, Interim equilibrium, Iterative deletion, Direct mechanism

Robust Implementation in Direct Mechanisms

A social choice function is robustly implementable if there is a mechanism under which the process of iteratively eliminating strictly dominated messages leads to outcomes that agree with the social choice function for all beliefs at every type profile. In an interdependent value envi­ronment with single crossing preferences, we identify a contraction property on the preferences which together with strict ex post incentive compatibility is sufficient to guarantee robust imple­mentation in the direct mechanism. Strict ex post incentive compatibility and the contraction property are also necessary for robust implementation in any mechanism, including indirect ones. The contraction property requires that the interdependence is not too large. In a linear signal model, the contraction property is equivalent to an interdependence matrix having all eigenvalues smaller than one.Mechanism design, Implementation, Robustness, Common knowledge, Interim equilibrium, Iterative deletion, Direct mechanism