Stable Coalition Structures in Simple Games with Veto Control

In this paper we study hedonic coalition formation games in which players' preferences over coalitions are induced by a semi-value of a monotonic simple game with veto control.We consider partitions of the player set in which the winning coalition contains the union of all minimal winning coalitions, and show that each of these partitions belongs to the strict core of the hedonic game. Exactly such coalition structures constitute the strict core when the simple game is symmetric.Provided that the veto player set is not a winning coalition in a symmetric simple game, then the partition containing the grand coalition is the unique strictly core stable coalition structure.Banzhaf value;hedonic game;semi-value;Shapley value;simple game;strict core

Enemies and Friends in Hedonic Games: Individual Deviations, Stability and Manipulation

We consider hedonic games with separable preferences, and explore the existence of stable coalition structures if only individual deviations are allowed.For two natural subdomains of separable preferences, namely preference domains based on (1) aversion to enemies and (2) appreciation of friends, we show that an individually stable coalition structure always exist, and a Nash stable coalition structure exists when mutuality is imposed.Moreover, we show that on the domain of separable preferences a contractual individually stable coalition structure can be obtained in polynomial time.Finally, we prove that, on each of the two subdomains, the corresponding algorithm that we use for finding Nash stable and individually stable coalition structures turns out to be strategy-proof.additive separability;coalition formation;hedonic games;stability;strategy-proofness

On the Axiomatic Characterization of "Who is a J?"

Recent work by Kasher and Rubinstein (1997) considers the problem of group identification from a social choice perspective.These authors provide an axiomatic characterization of a liberal aggregator whereby the group consist of those and only those individuals each of which views oneself a member of the group.In the present paper we show that the five axioms used in Kasher and Rubinstein s characterization of the liberal aggregator are not independent and prove that only three of their original axioms are necessary and sufficient for the required characterization.aggregation;group identification;axiomatic method

On Procedural Freedom of Choice

Numerous works in the last decade have analyzed the question of how to compare opportunity sets as a way to measure and evaluate individual freedom of choice.This paper defends that, in many contexts, external procedural aspects that are associated to an opportunity set should be taken into account when making judgements about the freedom of choice an agent enjoys.We propose criteria for comparing procedure-based opportunity sets that are consistent with both the procedural aspect of freedom and most of the standard theories of ranking opportunity sets.opportunity set;freedom of choice

Procedural Group Identification

In this paper we axiomatically characterize two recursive procedures for defining a social group.The first procedure starts with the set of all individuals who define themselves as members of the social group, while the starting point of the second procedure is the set of all individuals who are defined by everyone in the society as group members.Both procedures expand these initial sets by adding individuals who are considered to be appropriate group members by someone in the corresponding initial set, and continue inductively until there is no possibility of expansion any more.identification;social groups;social identity

The Equal Split-Off Set for Cooperative Games

In this paper the equal split-o. set is introduced as a new solution concept for cooperative games.This solution is based on egalitarian considerations and it turns out that for superadditive games the equal split-o. set is a subset of the equal division core.Moreover, the proposed solution is single valued on the class of convex games and it coincides with the Dutta-Ray constrained egalitarian solution.

Egalitarianism in Convex Fuzzy Games

In this paper the egalitarian solution for convex cooperative fuzzy games is introduced.The classical Dutta-Ray algorithm for finding the constrained egalitarian solution for convex crisp games is adjusted to provide the egalitarian solution of a convex fuzzy game.This adjusted algorithm is also a finite algorithm, because the convexity of a fuzzy game implies in each step the existence of a maximal element which corresponds to a crisp coalition.For arbitrary fuzzy games the equal division core is introduced.It turns out that both the equal division core and the egalitariansolution of a convex fuzzy game coincide with the corresponding equal division core and the constrained egalitarian solution, respectively, of the related crisp game.game theory

A New Characterization of Convex Games

A cooperative game turns out to be convex if and only if all its marginal games are superadditive.characterization;convex games;marginal games;superadditive games

Convex Games versus Clan Games

In this paper we provide characterizations of convex games and total clan games by using properties of their corresponding marginal games.We show that a "dualize and restrict" procedure transforms total clan games with zero worth for the clan into monotonic convex games.Furthermore, each monotonic convex game generates a total clan game with zero worth for the clan by a "dualize and extend" procedure.These procedures are also useful for relating core elements and elements of the Weber set of the corresponding games.convex games;core;dual games;marginal games;total clan games;Weber set

Good and Bad Objects: Cardinality-Based Rules

We consider the problem of ranking sets of objects, the members of which are mutually compatible.Assuming that each object is either good or bad, we axiomatically characterize three cardinality-based rules which arise naturally in this dichotomous setting.They are what we call the symmetric difference rule, the lexicographic good-bad rule, and the lexicographic bad-good rule.Each of these rules induces a unique additive separable preference relation over the set of all groups of objects.welfare economics;ranking