Carlos Pimienta

Undominated (and) perfect equilibria in Poisson games

In games with population uncertainty some perfect equilibria are in dominated strategies. We prove that every Poisson game has at least one perfect equilibrium in undominated strategies

Strategic stability in Poisson games

In Poisson games, an extension of perfect equilibrium based on perturbations of the strategy space does not guarantee that players use admissible actions. This observation suggests that such a class of perturbations is not the correct one. We characterize the right space of perturbations to define perfect equilibrium in Poisson games. Furthermore, we use such a space to define the corresponding strategically stable sets of equilibria. We show that they satisfy existence, admissibility, and robustness against iterated deletion of dominated strategies and inferior replies.

Generic finiteness of outcome distributions for two-person game forms with three outcomes ☆

A two-person game form is given by nonempty finite sets S1, S2 of pure strategies, a nonempty set [Omega] of outcomes, and a function [theta]:S1xS2-->[Delta]([Omega]), where [Delta]([Omega]) is the set of probability measures on [Omega]. We prove that if the set of outcomes contains just three elements, generically, there are finitely many distributions on [Omega] induced by Nash equilibria.

Generic determinacy of Nash equilibrium in network-formation games

This paper proves the generic determinacy of Nash equilibrium in network-formation games: for a generic assignment of utilities to networks, the set of probability distributions on networks induced by Nash equilibria is finite.

On stable outcomes of approval, plurality, and negative plurality games

We prove two results on the generic determinacy of Nash equilibrium in voting games. The first one is for negative plurality games. The second one is for approval games under the condition that the number of candidates is equal to three. These results are combined with the analogous one obtained in De Sinopoli (Games Econ Behav 34:270–286, 2001) for plurality rule to show that, for generic utilities, three of the most well-known scoring rules, plurality, negative plurality and approval, induce finite sets of equilibrium outcomes in their corresponding derived games—at least when the number of candidates is equal to three. This is a necessary requirement for the development of a systematic comparison amongst these three voting rules and a useful aid to compute the stable sets of equilibria Mertens (Math Oper Res 14:575–625, 1989) of the induced voting games. To conclude, we provide some examples of voting environments with three candidates where we carry out this comparison.

On the equivalence between (quasi-)perfect and sequential equilibria

We prove the generic equivalence between quasi-perfect equilibrium and sequential equilibrium. Combining this result with Blume and Zame (Econometrica 62:783–794, 1994) shows that perfect, quasi-perfect and sequential equilibrium coincide in generic games.

Costly Network Formation and Regular Equilibria

We prove that for generic network-formation games where players incur a strictly positive cost to propose links the number of Nash equilibria is finite. Furthermore all Nash equilibria are regular and, therefore, stable sets.

The structure of Nash equilibria in Poisson games

We show that many results on the structure and stability of equilibria in finite games extend to Poisson games. In particular, the set of Nash equilibria of a Poisson game consists of finitely many connected components and at least one of them contains a stable set (De Sinopoli et al., 2014). In a similar vein, we prove that the number of Nash equilibria in Poisson voting games under plurality, negative plurality, and (when there are at most three candidates) approval rule, as well as in Poisson coordination games, is generically finite. As in finite games, these results are obtained exploiting the geometric structure of the set of Nash equilibria which, in the case of Poisson games, is shown to be semianalytic.

Reaching consensus through approval bargaining

In the Approval Bargaining game, two players bargain over a finite set of alternatives. To this end, each one simultaneously submits a utility function u jointly with a real number α; by doing so she approves the lotteries whose expected utility according to u is at least α. The lottery to be implemented is randomly selected among the most approved ones. We first prove that there is an equilibrium where players truthfully reveal their utility function. We also show that, in any equilibrium, the equilibrium outcome is approved by both players. Finally, every equilibrium is sincere and Pareto efficient as long as both players are partially honest.

Reaching Consensus Through Simultaneous Bargaining

We propose a two-player bargaining game where each player simultaneously proposes a set of lotteries on a finite set of alternatives. If the two sets have elements in common the outcome is selected by the uniform probability measure over the intersection. If otherwise the sets do not intersect the outcome is selected by the uniform probability measure over the union. We show that this game always has an equilibrium in sincere strategies (i.e. such that players truthfully reveal their preferences). We also prove that every equilibrium is individually rational and consensual. If furthermore players are partially honest then every equilibrium is efficient and sincere. We use this result to fully characterize the set of equilibria of the game under partial honesty.