On the accessibility of core-extensions

Sengupta and Sengupta (1996) study the accessibility of the core of a TU game and show that the core, if non-empty, can be reached from any non-core allocation via a finite sequence of successive blocks. This paper complements the result by showing that when the core is empty, a number of non-empty core-extensions, including the least core and the weak least core (Maschler et al., 1979), the positive core (Orshan and Sudhölter, 2001) and the extended core (Bejan and Gómez, 2009), are accessible in a strong sense, namely each allocation in each of the foregoing core-extensions can be reached from any allocation through a finite sequence of successive blocks.     

On the Least Core and the Mas-Colell Bargaining Set

We show that the least core of a TU coalitional game with a finite set of players is contained in the Mas-Colell bargaining set. This result is extended to games with a measurable space of players in which the worth of the grand coalition is at least that of any other coalition in the game. As a consequence, we obtain an existence theorem for the Mas-Colell bargaining set in TU games with a measurable space of players. Journal of Economic Literature Classification Number: C71.     

Stability and Largeness of the Core

In general, there are examples of TU games where the core is stable but is not large. In this paper, we show that the extendability condition introduced by Kikuta and Shapley (1986, “Core Stability in n-Person Games,” Mimeo) is sufficient for the core to be stable as well as large, for TU games with five or fewer players. We provide a counter example when the number of players is six. We then introduce a stronger extendability condition and show that it is necessary and sufficient for the core to be large. Our proof makes use of a well-known result from the theory of convex sets. Journal of Economic Literature Classification Number: C71.     

On core stability, vital coalitions, and extendability

If a TU game is extendable, then its core is a stable set. However, there are many TU games with a stable core that are not extendable. A coalition is vital if there exists some core element x such that none of the proper subcoalitions is effective for x. It is exact if it is effective for some core element. If all coalitions that are vital and exact are extendable, then the game has a stable core. It is shown that the contrary is also valid for matching games, for simple flow games, and for minimum coloring games.     

On core stability,vital coalitions,and extendability

If a TU game is extendable, then its core is a stable set. However, there are many TU games with a stable core that are not extendable. A coalition is vital if there exists some core element x such that none of the proper subcoalitions is effective for x. It is exact if it is effective for some core element. If all coalitions that are vital and exact are extendable, then the game has a stable core. It is shown that the contrary is also valid for matching games, for simple flow games, and for minimum coloring games.     

A Note on Viable Proposals*

Sengupta and Sengupta (“Viable Proposals,”International Economic Review 35 (1994), 347–59.) consider a payoff vector of a TU‐game as a viable proposal if it challenges each legitimate contender. They show that for each game the set of viable proposals is nonempty. Their proof, however, has a flaw. I present a proof based upon a result by Kalai and Schmeidler (“An Admissible Set Occurring in Various Bargaining Situations,”Journal of Economic Theory 14 (1977), 402–11) .     

The bargaining set of a large game

We study the equivalence between the Mas-Colell bargaining set and the core in the general context of TU games with a measurable space of players. In the first part of the paper, we study the problem without imposing any restriction on the class of games we consider. In the second part, we first introduce a new class of exact games, which we call thin games. For these games, we show not only that the Mas-Colell bargaining set is equal to the core, but also that it is the unique stable set in the sense of von Neumann and Morgenstern. We then study the relation between thin games, exact non-atomic market games and non-atomic convex games. Finally, by further developing “thinness” related ideas, we prove new equivalence results for a class of non-exact market games as well as a class of non-exact, non-market games.     

The vector lattice structure of the n-person TU games

We show that any cooperative TU game is the maximum of a finite collection of a specific class of the convex games: the almost positive games. These games have non-negative dividends for all coalitions of at least two players. As a consequence of the above result we show that the class of modular games is a set of generators of the distributive lattice of all cooperative TU games. Finally, we characterize zero-monotonic games using a strong max-convex decomposition.     

Outside options,component efficiency,and stability

In this paper, we introduce a component efficient value for TU games with a coalition structure which reflects the outside options of players within the same structural coalition. It is based on the idea that splitting a coalition should affect players who stay together in the same way. We show that for all TU games there is a coalition structure that is stable with respect to this value.     

Payoffs in Nondifferentiable Perfectly Competitive TU Economies

We show that a single-valued solution of nonatomic finite-type market games (or perfectly competitive TU economies underling them) is uniquely determined as the Mertens value by four plausible value-related axioms. Since the Mertens value is always in the core of an economy, this result provides an axiomatization of a core-selection (or, alternatively, a competitive payoff selection). Journal of Economic Literature Classification Numbers: C71, D51, D61.     

A Theory of Gradual Coalition Formation

We study noncooperative multilateral bargaining games, based on underlying TU games, in which coalitions can renegotiate their agreements. We distinguish between models in which players continue to bargain after implementing agreements ("reversible actions") and models in which players who implement agreements must leave the game ("irreversible actions"). We show that renegotiation always results in formation of the grand coalition if actions are reversible, but that the process may otherwise end with smaller coalitions. On the other hand, we show that the grand coalition cannot form in one step if the core of the game is empty, irrespective of the reversibility of actions.     

ANTI‐DUAL OF ECONOMIC COALITIONAL TU GAMES*

Some well‐known coalitional TU (transferable utility) games applied to specific economic problems are shown to be connected through the relation defined as the anti‐dual. Solutions such as the core, the Shapley value and the nucleolus of anti‐dual games are obtained straightforwardly from original games.     

The Core of Large Differentiable TU Games

For suitable non-atomic TU games ν, the core can be determined by computing appropriate derivatives of ν, yielding one of two stark conclusions: either core(ν) is empty or it consists of a single measure that can be expressed explicitly in terms of derivatives of ν. In this sense, core theory for a class of games may be reduced to calculus. Journal of Economic Literature Classification Number: C71.     

A bargaining approach to the Owen value and the Nash solution with coalition structure

The mechanism by Hart and Mas-Colell (1996) for non-transferable utility (NTU) games is generalized so that a coalition structure among players is taken into account. The new mechanism yields the Owen value for transferable utility (TU) games with coalition structure as well as the consistent value (Maschler and Owen 1989, 1992) for NTU games with trivial coalition structure. Furthermore, we obtain a solution for pure bargaining problems with coalition structure which generalizes the Nash (1950) bargaining solution.     

Intermediate Preferences and Behavioral Conformity in Large Games

Motivated by Wooders, Cartwright, and Selten (2006) , we consider games with a continuum of players and intermediate preferences. We show that any such game has a Nash equilibrium that induces a partition of the set of attributes into a bounded number of convex sets with the following property: all players with an attribute in the interior of the same element of the partition play the same action. We then use this result to show that all sufficiently large, equicontinuous games with intermediate preferences have an approximate equilibrium with the same property. Our result on behavior conformity for large finite game generalizes Theorem 3 of Wooders et al. (2006) by allowing both a wider class of preferences and a more general attribute space.     

Deterrence and cooperation: A classification of two-person games

In two-person games in normal, bilateral threats succeed in self-enforcing any imputation. We discriminate among imputations by looking at various features of deterring threats. As a result we obtain a classification of two-person games. Finally a duopoly example is analysed.     

Inessentiality of large groups and the approximate core property: an equivalence theorem

Summary Inessentiality of large groups or, in other words, effectiveness of small groups, means that almost all gains to group formation can be realized by partitions of the players into groups bounded in absolute size. The approximate core property is that all sufficiently large games have nonempty approximate cores. I consider these properties in a framework of games in characteristic function form satisfying a mild boundedness condition where, when the games have many players, most players have many substitutes. I show that large (finite) games satisfy inessentially of large groupsif and only if they satisfy the approximate core property.This paper focuses on a part of another paper, Inessentiality of Large Coalitions and the Approximate Core Property; Two Equivalence Theorems, previously circulated as a University of Bonn Sonderforschungsbereich Discussion Paper.The author is indebted to Roger Myerson for a very stimulating comment and the term inessentiality of large coalitions. She is also indebted to Robert Anderson, Sergiu Hart, and Aldo Rustichini for helpful conversations. She is especially indebted to Robert Aumann for many stimulating and helpful discussions on research leading to this paper. The author gratefully acknowledges the financial support of the SSHRC and the hospitality and support of the University of Bonn through Sonderforschungsbereich 303.     

Cooperative games in permutational structure

Summary. By a cooperative game in coalitional structure or shortly coalitional game we mean the standard cooperative non-transferable utility game described by a set of payoffs for each coalition being a nonempty subset of the grand coalition of all players. It is well-known that balancedness is a sufficient condition for the nonemptiness of the core of such a cooperative non-transferable utility game. In this paper we consider non-transferable utility games in which for any coalition the set of payoffs depends on a permutation or ordering upon any partition of the coalition into subcoalitions. We call such a game a cooperative game in permutational structure or shortly permutational game. Doing so we extend the scope of the standard cooperative game theory in dealing with economic or political problems. Next we define the concept of core for such games. By introducing balancedness for ordered partitions of coalitions, we prove the nonemptiness of the core of a balanced non-transferable utility permutational game. Moreover we show that the core of a permutational game coincides with the core of an induced game in coalitional structure, but that balancedness of the permutational game need not imply balancedness of the corresponding coalitional game. This leads to a weakening of the conditions for the existence of a nonempty core of a game in coalitional structure, induced by a game in permutational structure. Furthermore, we refine the concept of core for the class of permutational games. We call this refinement the balanced-core of the game and show that the balanced-core of a balanced permutational game is a nonempty subset of the core. The proof of the nonemptiness of the core of a permutational game is based on a new intersection theorem on the unit simplex, which generalizes the well-known intersection theorem of Shapley. Received: October 31, 1995; revised version: February 5, 1997     

The law of supply in games, markets and matching models

Summary In large games with transferable utility, core payoffs satisfy a comparative statics property: If the proportion of one type of player increases, then the core payoff to that type of player decreases (does not increase). Markets with transferable utility satisfy a similar property: if the aggregate supply of a commodity increases, its value relative to the value of all commodities decreases. In market games, if one type of agent becomes more plentiful, his competitive payoff falls, and its decrease is engineered by a decrease in the relative value of his endowment.We thank Bob Anderson, Joe Farrell, Steve Goldman, Chris Shannon, seminar participants of the Mathematical Economics Seminar at Berkeley (August 1994), the University of Pittsburg (November 1994), Tel Aviv University and the Institute on Rationality at the Hebrew University (January 1995), and especially Vince Crawford for useful discussion.