Publications

Games and Economic Behavior, 2025, Volume 154: 16 - 52.

Abstract: We study hedonic coalition formation problems with friend-oriented preferences; that is, each agent has preferences over his coalitions based on a partition of the set of agents, except himself, into “friends” and “enemies” such that (E) adding an enemy makes him strictly worse off and (F) adding a friend together with a set of enemies makes him strictly better off. Friend-oriented preferences induce a so-called friendship graph where vertices are agents and directed edges point to friends.

We show that the partition associated with the strongly connected components (SCC) of the friendship graph is in the strict core. We then prove that the SCC mechanism, which assigns the SCC partition to each hedonic coalition formation problem with friend-oriented preferences, satisfies a strong group incentive compatibility property: group strategy-proofness. Our main result is that on any “rich” subdomain of friend-oriented preferences, the SCC mechanism is the only mechanism that satisfies core stability and strategy-proofness.


Business and Economics Research Journal, 2023, 14(3): 303 - 319.

Abstract: We consider hedonic coalition formation games. A hedonic coalition formation game is a pair which consists of a finite set of agents and a list of agents’ preferences such that each agent has preferences over all coalitions containing her. We study the existence of a Nash stable partition under different membership rights for anonymous and separable hedonic coalition formation games. We prove that for anonymous and separable hedonic games, the existence of a Nash stable partition is always guaranteed when the membership rights are Free Exit-Approved Entry or Approved Exit-Free Entry, but the existence of a Nash stable partition is not guaranteed when the membership rights are Free Exit-Free Entry. We also analyze the relation of the anonymity and separability with the other sufficient conditions which guarantee the existence of a Nash stable partition under different membership rights.


Journal of Business, Economics, and Finance, 2023, 12(1): 45 - 58.

Abstract: Purpose: We study hedonic coalition formation games in which each agent has preferences over the coalitions she is a member of. Hedonic coalition formation games are used to model economic, social, and political instances in which people form coalitions. The outcome of a hedonic coalition formation game is a partition. We consider stability concepts of a partition that are based on a single-agent deviation under different membership rights, that is, we study Nash stability under different membership rights. We revisit the conditions that guarantee the existence of Nash stable partitions and provide examples of hedonic coalition formation games satisfying these conditions. Methodology: While analyzing a stability notion for hedonic coalition formation games, two crucial points are considered: i) who can deviate from the given partition, ii) what are the allowed movements for the deviator(s), i.e., what deviators are entitled to do. For the first point, the deviation of a single agent is considered for Nash stabilities. For the second point, the allowed movements for deviators are determined by specifying membership rights, that is, membership rights describe whose approval is needed for a particular deviation. So, we reconsider stability concepts by using membership rights based on individual deviations, i.e., we consider Nash stability under different membership rights for hedonic coalition formation games. Findings: A classification of stability concepts based on a single-agent deviation for hedonic coalition formation games are provided by employing membership rights. The conditions in the literature guaranteeing the existence of Nash stable partitions for all membership rights are revisited. For each condition, an example of a hedonic coalition formation game satisfying the condition is given. Hence, a complete analysis of sufficient conditions for all Nash stability concepts are provided. Conclusion: To choose the correct stability notion one first should understand the membership rights in the environment that she studies. Then, for hedonic coalition formation problems, the appropriate Nash stability notion consistent with the ongoing membership rights should be chosen when single-agent deviation is considered.


Journal of Management and Economics Research, 2022, 20(4): 335 - 350.

Abstract: We study hedonic coalition formation games that consist of a finite set of agents and a list of agents' preferences such that each agent's preferences depend only on the members of her coalition. An outcome of a hedonic coalition formation game is a partition (i.e., coalition structure) of the finite set of agents. We study the existence of partitions that are both internally stable and Pareto optimal. We construct an algorithm that terminates for each given hedonic coalition formation game such that the outcome of the algorithm is internally stable and Pareto optimal. We also show that if the outcome of the algorithm is the partition that consists of singleton coalitions, then it is also core stable and if it is the partition that contains only the grand coalition then it is also both core stable and Nash stable.


Ankara University SBF Journal, 2022, 77(4): 853 - 875.

Abstract: This paper is on hedonic coalition formation games. We focus on a new stability concept called internal stability and introduce an algorithm that always brings internally stable coalition structures. Firstly, we analyze the relation between internal stability and other stability concepts. Then, we prove that the algorithm we introduce also brings non-trivial internally stable coalition structures in the full domain. Then, we analyze the relation between trivial coalition structures and the behavior of the algorithm.