Takumi Kongo

Whose deletion does not affect your payoff? The difference between the Shapley value, the egalitarian value, the solidarity value, and the Banzhaf value

This study provides a unified axiomatic characterization method of one-point solutions for cooperative games with transferable utilities. Any one-point solution that satisfies efficiency, the balanced cycle contributions property (BCC), and the axioms related to invariance under a player deletion is characterized as a corollary of our general result. BCC is a weaker requirement than the well-known balanced contributions property. Any one-point solution that is both symmetric and linear satisfies BCC. The invariance axioms necessitate that the deletion of a specific player from games does not affect the other players’ payoffs, and this deletion is different with respect to solutions. As corollaries of the above characterization result, we are able to characterize the well-known one-point solutions, the Shapley, egalitarian, and solidarity values, in a unified manner. We also studied characterizations of an inefficient one-point solution, the Banzhaf value that is a well-known alternative to the Shapley value.

Axiomatization of the Shapley value using the balanced cycle contributions property

This paper presents an axiomatization of the Shapley value. The balanced cycle contributions property is the key axiom in this paper. It requires that, for any order of all the players, the sum of the claims from each player against his predecessor is balanced with the sum of the claims from each player against his successor. This property is satisfied not only by the Shapley value but also by some other values for TU games. Hence, it is a less restrictive requirement than the balanced contributions property introduced by Myerson (International Journal of Game Theory 9, 169–182, 1980).

Difference between the Position Value and the Myerson Value is Due to the Existence of Coalition Structures

The study characterizes the position value and the Myerson value for communication situations. Each of these two values is represented by the Shapley value of a modified game obtained from the original communication situation. The difference between the two values comes from the existence of a coalition structure in the modified game.

An alternative axiomatization of the Hirsch index

We axiomatize the well-known Hirsch index (h-index), which evaluates researcher productivity and impact on a field, and formalize a new axiom called head-independence. Under head-independence, a decrease, to some extent, in the number of citations of “frequently cited papers” has no effect on the index. Together with symmetry and axiom D, head-independence uniquely characterizes the h-index on a certain domain of indices. Some relationships between our axiomatization and those in the literature are also investigated.

Value of games with two-layered hypergraphs

This paper studies cooperative games with restricted cooperation among players. We define situations in which a priori unions and hypergraphs coexist simultaneously and mutually depend on each other. We call such structures two-layered hypergraphs. Using a two-step approach, we define a value of the games with two-layered hypergraphs. The value is characterized by Owens coalitional value of hypergraph-restricted games and in terms of weighted Myerson value. Further, our value is axiomatically characterized by component efficiency and a coalition size normalized balanced contributions property.

NON-COOPERATIVE AND AXIOMATIC CHARACTERIZATIONS OF THE AVERAGE LEXICOGRAPHIC VALUE

We give a non-cooperative and an axiomatic characterization of the Average Lexicographic value (AL-value) on the class of balanced games. The AL-value is a single-valued solution for balanced TU-games. It is defined as the average of lexicographic maximum of the core of the game with respect to all orders on the player set, and it can be seen as a core selection based on the priority orders on the players. In both of our characterizations of the AL-value, a consistency property which we call average consistency plays an important role, and the property is obtained by the consistency property a la Davis and Maschler of the lexicographic vectors with respect to any order of players.

The balanced contributions property for symmetric players

This paper introduces a new relational axiom, the balanced contributions property for symmetric players, in TU cooperative games. It describes the fair treatment of symmetric players by restricting the requirement of the balanced contributions property to two symmetric players. Even under efficiency, our new axiom is logically independent of symmetry, which requires that symmetric players receive the same payoff. Nonetheless, in previous axiomatizations of an anonymous solution, replacing symmetry with our new axiom results in new axiomatizations of the solution.

Effects of Players’ Nullification and Equal (Surplus) Division Values

We provide axiomatic characterizations of the solutions of transferable utility (TU) games on the fixed player set, where at least three players exist. We introduce two axioms on players’ nullification. One axiom requires that the difference between the effect of a player’s nullification on the nullified player and on the others is relatively constant if all but one players are null players. Another axiom requires that a player’s nullification affects equally all of the other players. These two axioms characterize the set of all affine combinations of the equal surplus division and equal division values, together with the two basic axioms of efficiency and null game. By replacing the first axiom on players’ nullification with appropriate monotonicity axioms, we narrow down the solutions to the set of all convex combinations of the two values, or to each of the two values.

Further axiomatizations of Egghe's g-index

We provide three axiomatic characterizations of Egghes g-index, which measures a researchers scientific output based on the number of papers the researcher has published and the number of citations of each of the researchers papers. We formulate six new axioms for indexes, namely, tail independence (TA), square monotonicity (SM), the cap condition (CC), strong square monotonicity (SSM), increasing marginal citations (IMC), and increasing marginal citations+ (IMC+). Along with the two well-known axioms T1 and T2 (Woeginger, 2008a), the g-index is characterized by (i) T1, T2, TA, SM, and CC, (ii) T1, T2, TA, SSM, and IMC, and (iii) T1, TA, SM, and IMC+. Two out of three characterizations are obtained by adding axioms to our new characterization of the class of indexes satisfying T1, T2, and TA, which are defined as generalizations of the g-index. Thus, the remaining four axioms in our first and second characterizations—SM, CC, SSM, and IMC—distinguish the original g-index from other related indexes in the class. Furthermore, the independence of our axioms and that of Woegingers study is shown.

An incompatibility between recursive unanimity and strategy-proofness in two-sided matching problems

In this article, we study the incompatibilities for the properties on matching rules in two-sided many-to-one matching problems under responsive preferences. We define a new property called respect for recursive unanimity. This property requires that if every agent matches with its first choice among its really possible choices that are based on a recursive procedure like the well-known top trading cycles algorithm, then we should respect it. More precisely, given a matching problem, we exclude the agents whose first choices are satisfied without any discrepancy among them, and consider the restricted matching problems of the remaining agents. If we reach a state in which all agents are excluded by repeating this procedure, then we should respect the outcome. This property is weaker than stability and is stronger than respect for unanimity (that is also known as weak unanimity). We show that there are no strategy-proof matching rules that respect recursive unanimity.