The uniqueness of a reduced game in a characterization of the core in terms of consistency

In this paper, we examine the uniqueness of a reduced game in an axiomatic characterization of the core of transferable utility (TU) games in terms of consistency. Tadenuma [10] establishes that the core is the only solution satisfying non-emptiness, individual rationality, and consistency with respect to a natural reduced game due to Moulin [6]. However, the core satisfies consistency with respect to many other reduced games, including unnatural ones. Then we ask whether there are other reduced games that can be used to characterize the core based on the same three axioms. The answer is no: the Moulin reduced game is the only reduced game such that the core is characterized by the three axioms, since for any other reduced game, there is a solution that satisfies the three axioms, but it differs from the core. Many other unnatural reduced games cannot be used to characterize the core based on the three axioms. Funaki [4] provides another axiomatization of the core: the core is the only solution satisfying non-emptiness, Pareto optimality, sub-grand rationality, and consistency with respect to a simple reduced game similar to a so-called subgame. We show that the simple reduced game is the only reduced game that can be used to characterize the core by the four axioms.