Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

This paper considers the computational complexity of the design of voting rules, which is formulated by simple games. We prove that it is an NP-complete problem to decide whether a given simple game is stable, or not.

DOI： 10.1007/s11238-014-9422-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

This paper examines coalition formation problems from the viewpoint of mechanism design. We consider the case where (i) the list of feasible coalitions (those coalitions which are permitted to form) is given in advance; and (ii) each individual's preference is a ranking over those feasible coalitions which include this individual. We are interested in requiring the mechanism to guarantee each coalition the "right" of forming that coalition at least when every member of the coalition ranks the coalition at the top. We name this property coalitional unanimity. We examine the compatibility between coalitional unanimity and incentive requirements, and prove that if the mechanism is strategy-proof and respects coalitional unanimity, then for each preference profile, there exists at most one strictly core stable partition, and the mechanism chooses such a partition whenever available. Further, the mechanism is coalition strategy-proof and respects coalitional unanimity if, and only if, the strictly core stable partition uniquely exists for every preference profile.

DOI： 10.1007/s00182-012-0318-x

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

This note considers the equilibrium Outcomes of the preference revelation games in the general model of indivisible good allocation introduced by [Sonmez, T., 1999. Strategy-proofness and essentially single-valued cores. Econometrica 67, 677-689]. We adopt the concepts of coalitional equilibria and cores which are both defined in terms of the weak deviation or blocking by a prescribed class of admissible coalitions, We prove that if the solution which induces preference revelation games is individually rational and pareto optimal and the class of admissible coalitions is "monotonic," then the set of coalitional equilibrium outcomes coincides with the core. And we point out that the preceding analysis in the context of marriage problems [Gale, D., Shapley, L, 1962. College admissions and the stability of marriage. American Mathematical Monthly 69, 9-15] is hardly extended to the general model. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmateco.2008.08.007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

It is known that on some social choice and economic domains, a social choice function is coalition strategy-proof if and only if it is Maskin monotonic (e.g. Muller, E., and Satterthwaite, M., (1977). The equivalence of strong positive association and strategy-proofness. J. Econ. Theory, 14 pp412-18.). This paper studies the foundation of those results. I provide a set of conditions which is sufficient for the equivalence between coalition strategy-proofness and Maskin monotonicity. This generalizes some known results. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.econlet.2006.11.005

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

In a simple game, coalitions belonging to a given class are "absolutely powerful" while others have no power. We attempt to make this distinction operational. Toward this end, we propose two axioms on social choice correspondences, Strong Non-Discrimination and Exclusion. Strong Non-Discrimination describes circumstances under which certain coalitions, the losing coalitions, have no influence over social choice. Exclusion requires that there are situations in which certain coalitions, the winning coalitions, can exercise their power. We show that the weak core correspondence is the minimal correspondence satisfying Maskin Monotonicity and Strong Non-Discrimination. We also show that the weak core is the unique correspondence satisfying Nash implementability, Strong Non-Discrimination, and Exclusion. (C) 2003 Elsevier Inc. All rights reserved.

DOI： 10.1016/S0899-8256(03)00055-1

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Language：English   Publishing type：Research paper (scientific journal)  

In a general model of indivisible good allocation, Sönmez (1999) established that, whenever the core is nonempty for each preference profile, if an allocation rule is strategy-proof, individually rational and Pareto optimal, then the rule is a selection from the core correspondence, and the core correspondence must be essentially single-valued. This paper studies the converse claim of this result. I demonstrate that whenever the preference domain satisfies a certain condition of 'richness', if the core correspondence is essentially single-valued, then any selection from the core correspondence is strategy-proof (even weakly coalition strategy-proof, in fact). In particular, on the domain of preferences in which each individual has strict preferences over his own assignments and there is no consumption externality, such an allocation rule is coalition strategy-proof. And on this domain, coalition strategy-proofness is equivalent to Maskin monotonicity, an important property in implementation theory.

DOI： 10.1007/s003550200169

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICA-VERLAG GMBH & CO  

This paper examines the alpha-core of strategic games by means of the consistency principle. I provide a new definition of a reduced game for strategic games. And I define consistency (CONS) and two forms of converse consistency (COLONS and COCONS*) under this definition of reduced games. Then I axiomatize the alpha-core for families of strategic games with bounded payoff functions by the axioms CONS, COCONS*, weak Pareto optimality (WPO) and one person rationality (OPR). Furthermore, I show that these four axioms are logically independent. In proving this, I also axiomatize the alpha-individually rational solution by CONS, COLONS and OPR for the same families of games. Here the alpha-individually rational solution is a natural extension of the classical 'maximin' solution.

DOI： 10.1007/s001820100074

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

This paper studies (single-valued) solutions to housing markets [Shapley and Scarf, Journal of Mathematical Economics, 1 (1974) 23] with strict preferences. I show that a solution is monotonic if and only if it is coalition strategy-proof. I point out that the strong core solution is the only solution which is monotonic, individually rational and an onto function. (As Roth and Postlewaite [Journal of Mathematical Economics, 4 (1977) 131] showed, the strong core solution is single-valued when the preferences are strict.) This result follows from the above equivalence theorem and a preceding characterization of the strong core solution by Ma [International Journal of Game Theory, 23 (1994) 75]. My characterization sharpens Sonmez's [Journal of Mathematical Economics, 26 (1996) 429] similar result by weakening Pareto optimality to ontoness. I also provide some related results. A solution is strategy-proof and nonbossy if and only if it is monotonic. Thus the strong core solution is the unique solution which is strategy-proof, nonbossy, individually rational, and onto. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0165-4896(00)00062-7

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Language：English   Publishing type：Research paper (bulletin of university, research institution)   Publisher：Hokkaido University  

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