This paper presents a model of a trade of information such that resales of it are freely allowed, yet no agent has the incentive to resell after he acquired it. Agents can communicate with each other in advance of the trade, and make an agreement to prevent resales; but the agreement is not binding. The information can be shared in a set of agents only if the agreement is self-enforcing, and we call such a set of agents a resale-proof set. It is shown that sharing in a resale-proof set of the smallest size is the only outcome that is not dominated by any resale-proof set.

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We investigate general properties of weak domination in the Shapley-Scarf exchange model with indivisible goods. We prove that every weakly dominated allocation is weakly dominated by some competitive allocation. Furthermore, if an allocation does not weakly dominate some other allocation, it is a weakly dominated allocation or the two allocations are indifferent. By using these results, we show that every non-competitive allocation is weakly dominated by some competitive allocation. The nonempty strong core proves to be a von Neumann-Morgenstern solution. We give also a necessary and sufficient condition for the equivalence of the strong core and the competitive allocations.

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This paper discusses how a democratic state can emerge as a result of a social contract and how it evolves dynamically in a society with a public good that confronts the Prisoners' Dilemma. Individuals of the society play a game of institutional arrangements to establish a state in which there are two classes: an enforcer who collects tax and has punishing power and enforcees who pay tax. Our main result is that the state emerges with a positive probability if and only if the productivity of the society is lower than a certain level which is determined by the population and the marginal productivity of the public good, and that the state will disappear as soon as the productivity becomes greater than this critical level.

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We utilize a simple two-product-one-factor oligopoly model with n_i identical firms in industry i(i=1, 2). Assuming the concavity of the profit functions, this paper will establish, among other things, that (a) if firms behave “more collusively” in an industry, the individual outputs and the aggregate output of the industry diminish and the price increases. In particular, this allows us to compare the output levels corresponding to the competitive equilibrium, Cournot equilibrium and that in the collusive solutions. Another point we hope to stress is that (b) the aggregate profit of an industry and profits of individual firms may change rather counter-intuitively when behavioral rules of firms change.
In reference to (b) above, we will give somewhat unexpected results in which the aggregate profit of the first industry is smallest when all the firms in the industry (or in each of the two industries) cooperate, at an intermediate profit level when they act as Cournot oligopolists and largest when they act as price takers.

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This paper inquires into the effect of choice of protection means, tariffs or quotas, on the economy's protection level for a small country within a specific-factor model when the protection level is determined by the lobbying activities by each industry (non-cooperative game) or jointly by negotiations of all the industries concerned (cooperative game). We will see that strategic interaction among lobbying industries gives rise to non-equivalence between tariffs and quotas.

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This paper examines moral hazard problems where performance is unverifiable. In contrast to standard cases, traditional mechanisms fail to achieve the first best outcome if performance, the quality of the product here, is unverifiable.
This paper shows that, by using a third party, high quality products can be supplied under perfectly competitive prices and the first best outcome is achieved. Furthermore, the behavior of the third party which explained in this paper is consistent with the actual behavior of distributors. So we can conclude that distributors may contribute to assure the unverifiable qualities.
The mechanism explained here differs considerably from the traditional arguments concerning, for example, monitoring quality. Distributors do not have to observe levels of quality. The repeated game between producer and consumer, and the contract between producer and distributor both support this mechanism.

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