International Journal of Game Theory

Einy, Ezra; Moreno, Diego; Shitovitz, Benyamin

doi: 10.1007/s001820050094pmid: N/A

We study the core of a non-atomic game v which is uniformly continuous with respect to the DNA-topology and continuous at the grand coalition. Such a game has a unique DNA-continuous extension on the space B 1 of ideal sets. We show that if the extension is concave then the core of the game v is non-empty iff is homogeneous of degree one along the diagonal of B 1. We use this result to obtain representation theorems for the core of a non-atomic game of the form v=f^μ where μ is a finite dimensional vector of measures and f is a concave function. We also apply our results to some non-atomic games which occur in economic applications.

Vasin, Alexander

doi: 10.1007/s001820050095pmid: N/A

The known variants of the Folk theorem characterize the sets of equilibria for repeated games. The present paper considers dominance solutions of finitely repeated games and discounted supergames with perturbed payoff functions. The paper shows that for a normal form game the set of dominance solution payoff vectors of the T-fold repetitions converges to the set of feasible and individually rational payoffs as T tends to infinity and the perturbation value tends to 0. A similar theorem is proved for supergames as the discount factor tends to 1.

Zhao, Jingang

doi: 10.1007/s001820050096pmid: N/A

This paper provides a TU α-core existence result in a large class of normal form games. In the oligopoly markets of a homogeneous good, the TU α-core is non-empty if all profit functions are continuous and concave. In a general game, the existence of TU α-core follows from the weak separability, the compactness and convexity of choice sets, and the concavity and continuity of payoff functions.

(Burnovski), Moshe Bar Niv; Zang, Israel

doi: 10.1007/s001820050097pmid: N/A

A major issue within the realm of Antitrust policy is the regulation of existing monopolies. We describe a new potential indirect scheme for regulating a natural monopoly that arises from high entry cost. The approach involves minimal government intervention, and it is based on encouraging entry by offering to subsidize entry cost for potential competitors. We pose this issue as a four-stage non-cooperative game. Analysis of sub-game perfect Nash equilibria of the game reveals that the first best outcome is achieved as the unique equilibrium in which the monopolist prices at marginal cost and there is no entry. The regulation is “costless,” since no entry will occur and hence no subsidy will be paid.

Herings, P. Jean-Jacques; Vannetelbosch, Vincent J.

doi: 10.1007/s001820050098pmid: N/A

There exist three equivalent definitions of perfect Nash equilibria which differ in the way “best responses against small perturbations” are defined. It is shown that applying the spirit of these definitions to rationalizability leads to three different refinements of rationalizable strategies which are termed perfect (Bernheim, 1984), weakly perfect and trembling-hand perfect rationalizability, respectively. We prove that weakly perfect rationalizability is weaker than both perfect and proper (Schuhmacher, 1995) rationalizability and in two-player games it is weaker than trembling-hand perfect rationalizability. By means of examples, it is shown that no other relationships can be found.

Ritzberger, Klaus

doi: 10.1007/s001820050099pmid: N/A

This paper considers characterizations of perfect recall in extensive form games. It is shown that perfect recall can be expressed in terms of choices without any reference to infomation sets. When information sets are taken into account, it is decomposable into an ordering of information sets and that players do not forget what they knew nor what they did. Thus, if information sets are partially ordered, then perfect recall is implied by the player's inability to refine her information from the memory.

Davis, Douglas D.; Holt, Charles A.

doi: 10.1007/s001820050100pmid: N/A

This paper reports results of an experiment design ed to investigate the nature of cooperation and punishment. Subjects are matched in a series of two-person, two-stage games with a sequential equilibrium that supports first-stage cooperation with a credible threat of subsequent punishment. Participants sometimes used a consistent punish/reward strategy, and when they did, cooperation rates increased dramatically. The results thus contradict “payoff relevance”: second-stage behavior can be influenced by first-stage outcomes that have no effect on the payoff structure. Nevertheless, high cooperation rates were often not observed, even with a Pareto undominated “punishment” equilibrium in the second stage.

Stahl, Dale O.

doi: 10.1007/s001820050101pmid: N/A

We put forth a general theory of boundedly rational behavior and learning for symmetric normal-form games with unique symmetric Nash equilibria. A class of evidence-based behavioral rules is specified, which includes best-responding to a prior and Nash play. A player begins with initial propsenities towards the rules, and given experience over time adjusts his/her propensities in proportion to the past performance of the rules. We focus on scenarios in which the past distribution of play is revealed to all players. Confronting this theory with experimental data, we find significant support for rule learning and heterogeneity among participants.

Duffy, John; Feltovich, Nick

doi: 10.1007/s001820050102pmid: N/A

This paper presents experimental results from an analysis of two similar games, the repeated ultimatum game and the repeated best-shot game. The experiment examines whether the amount and content of information given to players affects the evolution of play in the two games. In one experimental treatment, subjects in both games observe not only their own actions and payoffs, but also those of one randomly chosen pair of players in the just-completed round of play. In the other treatment, subjects in both games observe only their own actions and payoffs. We present evidence suggesting that observation of other players' actions and payoffs may affect the evolution of play relative to the case of no observation.