Abstracts
Please note:
Many papers contain preliminary and possibly
incomplete results. Please contact the author(s) if you
find any errors, and do not cite without their permission.
The full author list is found in each paper.
Missing numbers are withdrawn papers where the presenter cannot
attend the conference.
Jump to abstract:
1 2 3 4 5 6 7 8 9
10 11 13 14 15 16 17 19
20 21 22 23 24 25 26 27 29
30 31 32 36 40 41 43 44 45 46 49
50 53 54 55 59
60 61 62 63 64 65 67 69
72 73 75 76 77 78 79
80 82 83 84 85 86 87 88 89
90 91 92 93 94 95 96 97 98 99
100 102 103 104 105 106 107
1 Josune
Albizuri: Coalitional Configurations and Value
In this work we suppose players in a cooperative game with
transferable utility are joined in coalitions and form any
collection of coalitions. In this framework we define and
characterize a value, which will be called configuration
value. When players form a partition of the set of players
this value coincides with the Owen value (1977), so it is a
generalization of the Owen value.
Talk time: Thursday 24 July,
3:00-3:25 Paper with full author
list: Stony03.pdf (8 kB)
Leniency clauses, offering cartelists legal immunity if they
blow the whistle on each other, is a recent anti-trust
innovation. The authorities wish to thwart cartels and
promote competition. This effect is not evident, however;
whistle-blowing may enforce trust and collusion by providing
a tool for cartelists to punish each other. We examine the
impact of leniency law, and other rules, theoretically and
experimentally.
Talk time: Monday 21 July,
3:35-4:00 Paper with full author
list: BlowingWhistle.pdf
(210 kB, revised June 4)
3 Jabier Arin:
Egalitarian Distributions for Coalitional Models: The Lorenz
Criterion
The paper presents a framework where the most important
single-valued solutions in the literature of TU-games are
jointly analyzed. It also suggests that similar frameworks
can be used in other coalitional models.
Talk time: Thursday 24 July,
3:35-4:00 Paper with full author
list: arin.pdf (251 kB)
4 Goksel Asan:
On the Stability and Optimality of Coalitions Voluntarily
Providing Impure Public Goods
We analyze the coalition formation in a society where every
coalition produces an excludable but possibly impure public
good by the voluntary contributions of its members. Agents
are allowed to make individual moves only while entry to and
exit from a coalition is free. In such a world and under the
absence of crowding effects, the set of stable and efficient
coalition structures coincide with the grand coalition. On
the other hand, this positive result about the
stability-efficiency equivalence collapses when the public
good is impure. In fact, there may be economies where the
set of stable and efficient coalition structures are
disjoint. However, tightening the membership property rights
by requiring the consent of all agents affected by an
individual move ensures that every efficient coalition
structure is stable, though the converse need not be true.
Talk time: Friday 25 July,
10:15-10:40 Paper with full author
list: AsanSanversbgt.pdf
(106 kB)
5 Siddhartha
Bandyopadhyay: Party Formation and Coalitional Bargaining in
a Model of Proportional Representation
We study a game theoretic model of a parliamentary democracy
under proportional representation. In our model, 'citizen
candidates' form parties prior to the election, voting takes
place and then governments are formed. If no single party
has an absolute majority, coalition governments may emerge
and we study the underlying coalition building process. The
type of government that is formed in equilibrium depends on
the parties' seat shares, the size of the rents that ruling
parties can extract from holding office and their
ideologies. We show that, depending on the relative
magnitudes of these factors, a variety of coalition
governments may result. Coalitions may be minimal; each
member of the coalition is necessary to retain the majority
or may contain some redundant parties. Moreover, coalitions
may be comprised of parties that are not adjacent in terms
of their ideology, that is, there may be a coalition
government made up of leftists and rightists from which
centrists are excluded. We then look at how the outcomes of
the coalition formation game affect the incentives for voter
groups to strategically form parties. We compare the results
of party formation under proportional representation with
that under the plurality rule. We show, in particular, that
Duverger's hypothesis that proportional representation leads
to more political competition than does the plurality rule
may not hold. Our model explains the diversity of electoral
outcomes observed empirically under proportional
representation.
Talk time: Thursday 24 July,
10:50-11:15 Paper with full author
list: revisingdraftpr.pdf
(301 kB)
6 Bradley
Belsky: Optimization Using Weighted Fictitious Play
Fictitious play is a model traditionally used to describe
learning. Players in a game assume that their opponents
have a fixed, but unknown mixed strategy. At each stage,
each player plays their best strategy assuming that every
other player uses as their mixed strategy the empirical
distribution of their past plays. A recent development of
fictitious play is its use as an optimization heuristic.
The belief distributions from the fictitious play heuristic
converge to the set of Nash Equilibrium, which we view as a
local optimum.
In this paper we investigate a modification to the
fictitious play optimization heuristic. When calculating
the empirical distribution of each player using standard
fictitious play, each stage is weighted equally. Players in
a game have no initial knowledge of their opponents mixed
strategies and are more likely to make strategic mistakes in
earlier stages. As the game progresses, the player begins
to learn their opponents mixed strategies as they converge
to the set of Nash Equilibrium. This intuition leads us to
believe that weighting later stages more than earlier stages
when calculating the empirical mixed strategy of all players
may lead to faster convergence.
This paper investigates truncating weighting schemes. In a
truncating weighting scheme weights are assigned to each
stages, however, at some point, the amount of weight
assigned to each play will be fixed. Numerous truncating
weighting schemes are investigated using randomly generated
games of various sizes. We compare results of the different
weighting schemes against standard fictitious play.
Talk time: Wednesday 23 July,
3:35-4:00 Paper with full author
list: belsk-abs.txt (3 kB)
We introduce a value for NTU games with coalition structure.
This value coincides with the consistent value for trivial
coalition structures, and with the Owen value for TU games
with coalition structure. Furthermore, we present two
characterizations: the first one using a consistency
property and the second one using balanced contributions'
properties.
Talk time: Monday 21 July,
3:00-3:25 Paper with full author
list: ntuccv.pdf (333 kB)
8 Ulrich Berger:
A General Model of Best Response Adaptation
I develop a general model of best response adaptation in
large populations for symmetric and asymmetric conflicts
with role-switching. For special cases, including the
classical best response dynamics and Cressman's symmetrized
best response dynamics, I show that the set of Nash
equilibria is attracting for zero-sum games. For any finite
two-player base game, if the populations are equally large,
convergence to a Nash equilibrium in the base game implies
convergence to a Nash equilibrium on the Wright manifold in
the role game.
Talk time: Monday 21 July,
10:50-11:15 Paper with full author
list: BergerUBRadapt.pdf
(266 kB)
9 Ulrich Berger:
Fictitious Play in 2xn Games
It is known that every continuous time fictitious play
process approaches equilibrium in every nondegenerate
2×2 and 2×3 game, and it has been conjectured
that convergence to equilibrium holds generally for
2×n games. We give a simple geometric proof of this.
As a corollary, we obtain the same result for the discrete
fictitious play process.
Talk time: Tuesday 22 July,
3:35-4:00 Paper with full author
list: fp2xnub.pdf (165 kB)
10 Steven
Brams: Voter Sovereignty and Election Outcomes
Voters are sovereign to the degree that they can express
their approval for any set of candidates. While voter
sovereignty is maximized under approval voting (AV), AV can
lead to
- a plethora of outcomes, depending on where voters
draw the line between acceptable and unacceptable
candidates; and
- Condorcet losers and other lesser
candidates, even in equilibrium.
But we argue that voters'
judgments about candidate acceptability should take
precedence over standard social-choice criteria, such as
electing a Condorcet or Borda winner. Among other things, we
show that
- sincere outcomes under all voting systems
considered are AV outcomes, but not vice versa;
- a Condorcet winner's election under AV is always a strong
Nash-equilibrium outcome but not under other systems; and
- outcomes that other systems cannot prevent can be prevented
under AV.
Talk time: Tuesday 22 July,
3:00-3:25 Paper with full author
list: Sovereignty.pdf (149 kB)
11 Yves
Breitmoser: Long-Term Equilibria of Repeated Consistently
Competitive Games
The class of consistently competitive games canonically
unifies Prisoner's Dilemmas, contests, auctions, and
Bertrand competitions. If those games are repeated
infinitely, the players have to negotiate about the
strategies that are to be repeated infinitely. These
negotiations, however, are perturbed by the possibility that
players make defective proposals (defective proposals are
sensibly not maintained in the long term). The opponents'
defections have to be detected and retaliated. In this
study, these aspects (negotiations and defections) are
analyzed jointly, and (thus) a refinement concept for Folk
theorem equilibria is introduced.
Talk time: Wednesday 23 July,
10:50-11:15 Paper with full author
list: compgame.pdf
(169 kB, revised June 20)
13 Eliane
Catilina: Absent-Minded Driver's Paradox: An Experiment
This paper searches for experimental evidence to the
absent-minded driver's paradox posed by Piccione and
Rubinstein (GEB, 1997a, P&R hereafter). Absent-mindedness
is defined as a form of imperfect recall where a player is
not able to recall if he/she has visited a decision node
before and thus, is not able "distinguish between two
histories on the same path" (P&R, p. 5).
Talk time: Monday 21 July,
3:00-3:25 Paper with full author
list: absentminded.pdf (7 kB)
Sellers benefit on average from revealing information about
their goods to buyers, but the incentive to exaggerate
undermines the credibility of seller statements. When
multiple goods are being auctioned, we show that revealing a
complete or partial ordering of the different goods by value
can be credible. Ordinal cheap talk of this form is not
susceptible to exaggeration because it simultaneously
reveals favorable information about some goods and
unfavorable information about other goods. Any informative
ordering increases revenues in accordance with the linkage
principle, and the complete ordering is asymptotically
revenue-equivalent to full revelation as the number of goods
becomes large. These results provide a new explanation in
addition to bundling, complementarities, and versioning for
how a seller benefits from the sale of multiple goods.
Talk time: Monday 21 July,
3:35-4:00 Paper with full author
list: sellercheaptalk.pdf
(303 kB, revised July 9)
15 Alfredo Di
Tillio: Subjective Expected Utility in Games
A model of subjective expected utility in games is
constructed in the spirit of Savage. First, the problem of
establishing what is a state of the world for a player is
solved: The result is a "universal space of acts",
constructed hierarchically, where preference relations, and
their axioms, are naturally induced from simpler objects.
Second, a representation theorem is given: Here the
hierarchical structure provides the appropriate cardinality,
especially important for uniqueness of the representation.
Third, game-theoretic results - e.g. the relationship with
existing solution concepts - will then be discussed: This
part is, however, still at a very preliminary stage.
Talk time: Thursday 24 July,
3:00-3:25 Paper with full author
list: subjectiveSB.pdf (50 kB)
16 Irinel
Dragan: The Least Square Values and the Shapley Value
The Least Square Values of cooperative TU games (briefly
LS-values), were found as solutions of an optimization
problem on the preimputation set (M.Keane, 1969). L.Ruiz,
F.Valenciano and J.Zarzuelo have axiomatized the LS-values
and discussed many properties (GEB, 1998). In earlier papers,
we have shown that the Banzhaf value (Dragan, 1996) and all
Semivalues (Dragan, 1999) are Shapley values of games easily
derived from a given game. In the present paper, we prove
that an LS-value of a given game is also a Shapley value of
a game easily derived from the given one. To do this we
derive an Average per capita formula for LS-values, very
similar to that obtained earlier for the Shapley value
(Dragan, 1991). A computational algorithm for Semivalues
follows and, a theoretical result, the relationship with
the Shapley value is obtained. Further, a potential basis
for the space of TU games is shown and from this, like in
the case of the Shapley value, we solve the inverse problem:
given an n- vector, find out the set of games for which the
LS-value equals the given vector. The inverse problem was
earlier solved for the Shapley value and the Weighted
Shapley value (Dragan, 1991).
Talk time: Wednesday 23 July,
3:00-3:25 Paper with full author
list: dragan.txt (3 kB)
Here we examine the process of discretizing an evolutionary game.
First, we change the replicator equation of game theory into a
Lotka-Volterra population equation. Then we use the technique
developed by Bettelheim, Agam and Shnerb to turn the
continuous Lotka-Volterra equation into a discrete version. This
involves treating the Lotka-Volterra equation as a mean field
equation and using techniques from quantum field theory and
statistical mechanics.
Talk time: Wednesday 23 July,
3:00-3:25 Paper with full author
list: gameconfpaper.pdf
(1082 kB)
19 Ori
Haimanko: On Continuity of the Equilibrium and Core
Correspondences in Economies with Differential Information
We study upper semi-continuity of correspondences of
several solution concepts for economies with differential
information, with Boylan (1971) topology on agents'
information fields. Radner (1958, 1982) introduced the
notion of competitive equilibrium for economies with
differential information by requiring agents' trades to be
measurable with respect to their respective information
fields. We show that in economies for which the (contingent)
commodity space is in a class of certain classical Banach
spaces, the Radner equilibrium correspondence is upper
semi-continuous. For a related ex ante core concept, the private
core (Yannelis 1991, Allen 1993), it is shown that the core
correspondence may not be upper semi-continuous. An
interim core concept, the coarse core (Wilson 1978), also
does not lead to an upper semi-continuous core
correspondence.
Talk time: Thursday 24 July,
10:15-10:40 Paper with full author
list: abs-einy.pdf (51 kB)
This paper suggests a mechanism for coordination by which
positional concerns might evolve endogenously. A generalized
2x2 Hawk-Dove game, which comprises Battle of the sexes, is
analyzed in an evolutionary environment where a continuum
of agents is randomly matched against each other. Status is
here defined by the agents' performance in previous games.
The agents' are assumed to have the ability to make an
imperfect observation on how their own status relates to
that of their opponent. These observations are then utilized
as an instrument for coordinating the strategies in the
game by the conditioning of the pure strategies on whether
the opponent has a higher status or a lower status. Since
this model implies that a conditioned strategy does not
necessarily correspond to a homogenous payo¤, a modified
version of ESS is introduced by which evolutionary stability
is determined. From this criterion it is shown that, as the
agent's observational skills come close to being perfect,
there exist three evolutionary stable strategies, two
conditioned and one unconditioned. It is then assumed that
these stable strategies can evolve and grow separately in
di¤erent isolated populations and that the each population
grows in proportion to its average payoff. Eventually, as
they grow larger, two populations are assumed to encounter
each other and merge into one. At this point it is assumed
that the adjustment process of the distribution is much
quicker than the growth process that in turn is much faster
than the mutations. As the criterion defined above is
yet again utilized to determine which strategy is
evolutionarily stable. It is shown that just one strategy
can survive; behave hawkish against less successful
opponents and dovish against more successful opponents.
Moreover it is also shown that this strategy will prevail
against strategies conditioned through other personal
characteristics such as e.g. size, and gender.
Talk time: Thursday 24 July,
3:00-3:25 Paper with full author
list: CTS.pdf
(499 kB, revised July 16)
21 Dragan
Filipovich: Ambiguous Contracting: Natural Language and
Judicial Interpretation
We study the relationship between ambiguity (which comes
into the picture since contracts have to be written in
natural language), and contractual incompleteness. The
contracting process is modelled as a signalling game between
the parties and the judge, with the contract as the signal.
The judge is assumed to be bound by the content of the
contract (in as far as it can be ascertained unambiguously).
Two kind of examples are presented: The first set of
examples shows how ambiguity can lead to incompleteness.
Here incompleteness is a way of hedging against adverse
judgements on the part of an imperfectly informed judge. The
remaining example illustrates a sort of converse intuition:
It shows how incompleteness might lead the contracting
parties to write ambiguous contracts in order to afford a
relatively well-informed judge freedom to enforce the
parties' will.
Talk time: Tuesday 22 July,
10:15-10:40 Paper with full author
list: ambiguouscontracts.pdf
(369 kB)
22 Julio González
Díaz: From Set-Valued Solutions to Single-Valued Solutions:
the Centroid
We study a general procedure which, given a set-valued
solution of a TU game, provides a single-valued solution.
Our solution inherits the properties of the set-valued
solution. If a set of allocations is chosen based on some
principles that a solution should satisfy, the single
allocation that we select is consistent with those
principles. Besides, it has a central position with respect
to the set, to be precise, it is the center of gravity
(centroid) of the set valued solution. Afterwards we
analyze this solution concept for some classical set valued
solutions, mainly in the core. Furthermore, we try to
establish a direct connection between the Centroid and the
Shapley Value.
Talk time: Thursday 24 July,
10:15-10:40 Paper with full author
list: centroid.pdf (75 kB)
23 Ziv
Gorodeisky: Evolutionary Stability for Large Populations and
Backward Induction
It has been shown (Hart [2002]) that the backward induction
(or subgame-perfect) equilibrium of a perfect information
game is the unique stable outcome for dynamic models
consisting of selection and mutation, when the mutation rate
is low and the populations are large, under the assumption
that the expected number of mutations per generation is
bounded away from zero. Here it is shown that one can
dispense with this last condition. In particular, it
follows that the backward induction equilibrium is
evolutionarily stable for large populations.
Talk time: Tuesday 22 July,
10:50-11:15 Paper with full author
list: paper.pdf (230 kB)
Can comparative statements be credible even when absolute
statements are not? For instance, can a professor credibly
rank different students for a prospective employer even if
she has an incentive to exaggerate the merits of each
student? Or can an analyst credibly rank different stocks
even if the client would be dubious about a recommendation
to buy any one of them? We examine such problems in a
multidimensional sender-receiver game where the sender has
private information about multiple variables. We show that
ordinal cheap talk, in which the variables are completely
ordered by value or grouped into categories by value, can be
credible even when interests are too opposed to support
communication along any single dimension. Ordinal cheap talk
is credible because it reveals both favorable and
unfavorable information at the same time, thereby precluding
any possibility of exaggeration. The communication gains
from ordinal cheap talk can be substantial with only a
couple of dimensions, and the payoffs from a complete
ordering are asymptotically equivalent to full revelation as
the number of variables becomes large. However, in some
circumstances the sender can do better through a partial
ordering that categorizes variables. Compared to other forms
of cheap talk, ordinal cheap talk is exceedingly simple in
that the sender only makes straightforward, comparative
statements.
Talk time: Tuesday 22 July,
10:15-10:40 Paper with full author
list: ordinal.pdf
(328 kB, revised July 9)
25 Dorothea
Herreiner: Envy as a Secondary Criterion of Fairness
In the recent experimental literature several utility models
have been suggested that address observed behavior not
reducible to the pursuit of self-interest. Most models are
based on some kind of social preferences, where the payoff
distribution is relevant for an individual's utility. Envy
is an important criterion in the theoretical literature on
fair division, whose definition differs from the more casual
usage of the word envy in the experimental literature. We
analyze several fair division problems where envy a la Foley
(1963) and social preferences can be distinguished. Envy is
shown to matter, although only as a secondary criterion.
Talk time: Monday 21 July,
10:15-10:40 Paper with full author
list: dorothea.txt (1 kB)
Auctions are considered with a (non-symmetric)
independent-private-value model of valuations. It shall be
demonstrated that a utility equivalence principle holds for
an agent if and only if she has constant absolute risk
aversion.
Talk time: Thursday 24 July,
3:35-4:00 Paper with full author
list: utilpap2.pdf (163 kB)
As opposed to the classical voting system (one person - one
decision - one vote) a new voting system is defined where
agents are endowed with a given number of votes that can be
distributed freely between a prearranged number of issues
that have to be approved or dismissed. Its essence relies on
allowing voters to express the intensity of their
preferences in a simple and applicable manner. From a
mechanism design perspective we first prove which
allocations are implementable: for a social choice function
to be implementable it should only care about the voter
relative intensities between the issues at the interim
stage. We also prove that this new voting system,
Qualitative Voting, Pareto dominates Majority Rule in some
general settings and, even more, it achieves the only
ex-ante incentive compatible optimal allocation. Finally, an
argument in favour of Majority Rule is presented showing
that the optimal implementable allocation robust to any
possible prior is the one achieved by Majority Rule.
Talk time: Tuesday 22 July,
3:35-4:00 Paper with full author
list: QualitativeVotingAbstract.pdf
(470 kB, revised July 9)
29 Stefan
Imhof: Stable Sequences of Political Coalitions
This paper explores a sequential coalition formation game
among political parties. We introduce the non-cooperative
concept of stable sequences of coalitions, a general
solution to sequential coalition formation games. The main
results are i) the order of the agenda matters for the
equilibrium outcome, ii) punishment strategies can support
otherwise unstable coalition structures, in particular the
phenomenon of ``strange bedfellows'' can arise in the first
round, and iii) a party which is median in all decisions is
always better off in the sequential game than in a single
coalition formation over two decisions, while the converse
is not true.
Talk time: Monday 21 July,
3:35-4:00 Paper with full author
list: Imhofgames03.pdf
(57 kB, revised May 16)
30 Elena
Inarra: The Supercore for Normal Form Games
We study the supercore of a system derived from a normal
form game. For the case of a finite game, we define a
sequence of games and show that the supercore coincides with
the set of Nash equilibrium strategy profiles of the last
game in that sequence. This result is illustrated with the
characterization of the supercore for the n-person
prisoner's dilemma. With regard to the mixed extension of a
game we prove that the supercore coincides with the set of
NE whenever the game has a finite number of Nash equilibria.
This coincidence is not mantained for games with infinite
Nash equilibria.
Talk time: Monday 21 July,
10:15-10:40 Paper with full author
list: AE.pdf
(235 kB, revised June 18)
31 Sergei
Izmalkov: Multi-unit Open Ascending Price Efficient Auction
In this paper I present an open ascending price mechanism
that allocates efficiently K identical objects among N
bidders with interdependent values. The mechanism consists
of a number of sequential English auctions with reentry and
has the following attributes. In each of the individual
auctions all the bidders compete simultaneously in the open
ascending price format. The most distinctive feature of the
mechanism is that winners are determined first, and then
additional auxiliary auctions are conducted to determine
prices. Total number of auctions depends only on the number
of goods to be allocated and not on the number of bidders.
Talk time: Tuesday 22 July,
3:00-3:25 Paper with full author
list: Izmalkov-abstract.txt
(1 kB)
32 Yuan Ju:
A Compensation Rule for Project-Allocation Games
In this paper, by introducing the notions of project and
proportion, we construct a simple cooperative game
theoretical framework for studying a class of economic
environments in which agents, with their initial endowments
(specialities and proportions of projects), would work
together in a joint program with one or a number of
projects. In addition to studying the effects of the
structures of coalitions, projects and proportions on
surplus sharing, we mainly focus on the problems of
compensation in cooperation. Taking the Shapley value as the
benchmark, we propose a general compensation rule by which
the compensator, compensatee and amount of compensation can
be easily specified in a just way. Moreover, we
characterize it as the unique compensation rule satisfying
efficiency, symmetry, dummy player, additivity and equity.
The usefulness of the framework is further illustrated by an
application in the field of public sector reforms, for which
we use a core-peripheral project-allocation model to
investigate the problems of compensation and show that the
competitiveness/bargaining power comparison among players
determines the direction and the amount of compensation.
Finally, we make an extension of the model and refine the
compensation rule.
Talk time: Wednesday 23 July,
3:35-4:00 Paper with full author
list: AbstractJu.pdf (78 kB)
36 Grigol
Kharabadze: End of Boeing's Monopoly: How Does Airbus' A380
Introduction Affect Large Commercial Aircraft Industry?
Since the first delivery of the 747, Boeing has been
enjoying monopoly power in the largecommercial aircraft
industry. As Airbus launches the A380 superjumbo, the
monopoly era of Boeing seems to be over. The main questions
this project will try to answer are: (1) how the entry of
Airbus' A380 will affect the large commercial aircraft
industry, i.e., how Boeing and Airbus will divide market
share in this Incumbent-Entrant game; and (2) how big is the
effect of the aid from European governments to Airbus.
The motivation for this research project is the tension
between two major civilian aircraft producers - The Boeing
Company and Airbus1. Corporate tensions reached a new level
after Airbus officially announced its plans for the A380
superjumbo - world's largest commercial aircraft.
The first A380 is due to be delivered in March 2006. This is
the beginning of the end of Boeing's more than 30 years of
exclusive monopoly in the large commercial aircraft industry.
Tensions do not have only corporate character. Introduction
of A380 adds another chapter in United States - European
Union history of trade disputes. The A380 development is a
$10.7 billion project, about one-third of which will be
funded by European governments - members of the Airbus
consortium. The United States has warned the European Union
that any additional loans that European government - members
will be making to Airbus to help fund the development of the
A380 must be at the market rates in order not to violate the
US - EC 1992 bilateral agreement.
In spite of all these corporate and political disputes, we
believe that the questions this research project addresses
can be usefully examined in terms of economic theory of
market entry and incumbent response. The paper provides a
simple and interesting approach to the problem of market
division.
Talk time: Thursday 24 July,
10:50-11:15 Paper with full author
list: AbstractGameTheoryConference.pdf
(46 kB)
40 László
Kóczy: The Minimal Dominant Set is a Non-Empty Core-Extension
A set of outcomes for a TU-game in characteristic function
form is dominant if it is, with respect to an
outsider-independent dominance relation, accessible (or
admissible) and closed. This outsider-independent
dominance relation is restrictive in the sense that a
deviating coalition cannot determine the payoffs of those
coalitions that are not involved in the deviation. The
minimal (for inclusion) dominant set is non-empty and for a
game with a non-empty coalition structure core, the minimal
dominant set returns this core.
Talk time: Thursday 24 July,
10:15-10:40 Paper with full author
list: koczylauwersmindomset.pdf
(203 kB)
41 Frederic
Koessler: Communication Equilibria with Partially Verifiable
Types
This paper studies the set of equilibria that can be
achieved by adding general communication systems to Bayesian
games in which some information can be certified or,
equivalently, in which players' types are partially
verifiable. Given the information that players are able to
certify, we characterize outcome-equivalent canonical
equilibria for which generalized versions of the revelation
principle are valid. Communication equilibria and associated
canonical representations are obtained as special cases
when no information can be certified.
Talk time: Tuesday 22 July,
3:00-3:25 Paper with full author
list: koessler.pdf (255 kB)
43 R. Vijay
Krishna: Absence of Commitment in Principal-Agent Games
We study the instances of Principal-Agent games where the
Principal cannot commit to the outcome prescribed by a
mechanism. This means that the Revelation Principle does not
hold. We exhibit a "cheap", pre-play procedure whereby, in a
certain class of games, the players can virtually implement
(in the absence of a mediator) a large subset of the
equilibria implementable with the help of a mediator.
Talk time: Monday 21 July,
10:15-10:40 Paper with full author
list: comm-abs.pdf (123 kB)
We investigate the behavior of players in a common interest
strategic form game who do not communicate with each other.
Moreover, the players do not know the utilities at the start
of the game, but learn them as the game is repeatedly
played. Each player assumes that the other players employ a
fixed but unknown mixed strategy. At each stage of the game,
the players simultaneously play their best response against
their belief distributions for the other players, which they
derive from the past history of plays. Unlike fictitious
play in which the players are assumed to know the entire
utility function, the players in this game base their best
response decisions on their current, possibly incomplete,
knowledge of the utility. We demonstrate that the sequence
of belief distributions converges to the set of Nash
equilibria. This concept is illustrated through an example
that we call "the FBI-CIA Game".
Talk time: Tuesday 22 July,
10:15-10:40 Paper with full author
list: kutmanabstract.pdf
(4 kB)
Two players compete in a number of simultaneous races in
different locations. The players have limited resources and
must decide how to allocate these to the different races. At
each location the player who allocates more resources wins
the prize corresponding to that location. As an example,
consider two candidates for election who must allocate their
campaign budgets to different states. Alternatively,
consider an R and D race in which multiple patents can be
won. Such games correspond to budget constrained
multiple-object all-pay auctions and constitute
non-zero-sum counterparts of Colonel Blotto type games
introduced by Borel. I analyze a class of such games with
complete information. Budget-constrained bidders
simultaneously submit vectors of bids from a convex set of
pure strategies, and the highest bidder at each location
wins that item. The presence of the budget constraint leads
to the indirect 'substitutability' among the objects: a
higher bid for one object leaves less resources for others.
I fully characterize the mixed-strategy equilibria in the
case of two bidders and two objects for the following cases
(i) identical values for the objects and identical budgets;
(ii) different common values but identical budgets; (iii)
identical values but different budgets. The results may be
generalized for an arbitrary number of objects.
Talk time: Wednesday 23 July,
3:35-4:00 Paper with full author
list: Kvassov.pdf (22 kB)
46 Theodore
Lambert: Fictitious Play Approach to a Mobile Unit Situation
Awareness Problem
Until now the fictitious play approach to optimization has
only been demonstrated on a dynamic traffic routing problem;
therefore, it is necessary to apply this method to other
problems in order to demonstrate its effectiveness as a
heuristic optimization method. We used the large scale
situational awareness simulation developed for the
Multidisciplinary University Research Initiative (MURI) on
``Low-Energy Electronic Design for Mobile Platforms'' to
test the fictitious play approach, since we already
possessed bench mark solutions from a simulated annealing
approach previously applied. We found that the fictitious
play approach yielded similar solutions to simulated
annealing and required comparable computational effort,
while they both outperformed pure random search. This
demonstrates the effectiveness of a fictitious play approach
to optimization for the large scale situational awareness
simulation, providing additional evidence as to fictitious
play's value as an optimization heuristic.
Talk time: Thursday 24 July,
10:50-11:15 Paper with full author
list: FictMuri.pdf (102 kB)
49 Qihong Liu:
Customer Information Sharing Among Rival Firms
The recent rapid growth of the Internet as a medium of
communication and commerce, combined with the development of
sophisticated software tools, are to a large extent
responsible for producing a new kind of information:
databases with detailed records about consumers'
preferences. These databases have become part of a firm's
assets, and as such they can be sold to competitors. This
possibility has raised numerous concerns from consumer
privacy advocates and regulators, who have entered into a
heated debate with business groups and industry associations
about whether the practice of customer information sharing
should be banned, regulated, or left unchecked. This paper
investigates the incentives of rival firms to share their
customer-specific information and evaluates the welfare
implications if such exchanges are banned, in the context of
a perfect
Talk time: Friday 25 July,
10:15-10:40 Paper with full author
list: liuserfes.pdf
(49 kB, revised June 2)
50 Xiao Luo:
A Unified Approach to Information, Knowledge, and Stability
Within the context of strategic interaction, we provide a
unified framework for analyzing information, knowledge, and
the "stable" pattern of behavior. The major innovations are:
(i) unlike the standard ad hoc semantic model of knowledge,
the state space is constructed by Harsanyi's types that were
explicitly formulated by Epstein and Wang (Econometrica 64,
1996, 1343-1373); (ii) players may be boundedly rational and
have non-partitional information structures; and (iii)
players may have general preferences, including subjective
expected utility and non-expected utility. We first study
the interactive epistemology. We then establish an
equivalence theorem between a strictly dominated strategy
and a never-best reply in terms of epistemic states.
Finally, we explore epistemic foundations behind the
fascinating idea of stability due to J. von Neumann and O.
Morgenstern.
Talk time: Tuesday 22 July,
3:35-4:00 Paper with full author
list: xluo.pdf
(374 kB, revised June 16)
53 Timothy
Mathews: Non-Binding Sequential Exchange Between Discounting
Agents
When exchange is sequential, and no binding agreements can be
written, the agent acting first is exposed to the possibility
that, even if he honors the agreement, his trading partner may
subsequently choose not to do so. The primary focus of the current
analysis is whether trade can successfully occur in such
environments. Exchange will successfully occur so long as there
are sufficiently large gains from trade for the agent acting
second. As a result, the agent acting first may be better off with
less relative bargaining power.
The possibility of facilitating exchange through the use of an
escrow service is considered. Conditions are determined under
which the agent acting first will employ such a service in order
to ensure successful exchange (as opposed to ensuring successful
exchange through the disposal of his own relative
bargaining advantage).
Talk time: Wednesday 23 July,
10:15-10:40 Paper with full author
list: MathewsPaper2.pdf
(360 kB)
54 Takashi
Matsuhisa: Rational Expectations Equilibrium in Economy for
Multi-Modal Logic
This article relates economies and traders' knowledge. We
consider a pure exchange economy under uncertainty where
the traders are assumed to have a non-partitional
information structure. The purpose is to propose the notion
of generalized rational expectations equilibrium for the
economy, and we investigate welfare in the economy with
emphasis on epistemic point of view. It is shown that
Theorem 1: There exists a generalized rational expectations
equilibrium for the economy. We shall characterize welfare
under the generalized rational expectations equilibrium:
Theorem 2: An allocation is ex-ante Pareto optimal if and
only if it is a generalized rational expectations
equilibrium allocation relative to some price system.
Talk time: Friday 25 July,
10:15-10:40 Paper with full author
list: Matsuhisa.pdf (168 kB)
We analyze Hotelling's duopoly model on the plane. There are
two players (firms) located in different points inside a
circle and the customers are distributed with some density
in it. The solution of two game-theoretic problems is
derived. The first problem is to find the equilibrium prices
for the homogeneous goods, and the second problem is to find
the equilibrium allocation of the players inside the circle.
The equilibrium in location game is constructed for uniform
and non-uniform case.
Talk time: Wednesday 23 July,
3:00-3:25 Paper with full author
list: Locator.pdf (186 kB)
59 Stefan
Napel: Power Measurement as Sensitivity Analysis - A Unified
Approach
This paper proposes a unified framework that integrates the
traditional index-based approach and the competing
non-cooperative approach to power analysis. It rests on a
quantifiable notion of ex post power as the (counterfactual)
sensitivity of the expected or observed outcome to
individual players. Thus, it formalizes players' marginal
impact on outcomes in both cooperative and non-cooperative
games, for both strategic interaction as well as purely
random behavior. By taking expectations with respect to
preferences, actions, and procedures one obtains meaningful
measures of ex ante power. Established power indices turn
out to be special cases.
Talk time: Wednesday 23 July,
3:35-4:00 Paper with full author
list: NapelWidgrenPaper.pdf
(305 kB)
60 Daniel
Neill: Cooperation and Coordination in the Turn-Taking Dilemma
In many real-world situations, "cooperation" in the simple
sense of the Prisoner's Dilemma is not sufficient for
success: instead, cooperators must precisely coordinate more
complex behaviors in a noisy environment. We investigate
one such model, the Turn-Taking Dilemma (TTD), a variant of
the repeated Prisoner's Dilemma in which the highest total
payoff is achieved not by simultaneous mutual cooperation,
but by taking turns defecting (alternating temptation and
sucker payoffs). The TTD more accurately models
interactions where players must take short-term losses for
long-term gains: situations marked by the intricate
give-and-take of bargaining and compromise. Using
"evolutionary dominance" as a general measure of
performance, we investigated which strategies are most
successful in TTD interactions. Top TTD strategies such as
EXALT_2 can effectively coordinate turn-taking under noise,
while exploiting cooperators and resisting exploitation by
defectors; these strategies are likely to achieve success in
the variety of real-world interactions modeled by the TTD.
Talk time: Tuesday 22 July,
3:00-3:25 Paper with full author
list: ttdconf.pdf (230 kB)
61 Ricardo
Nieva: Coase, an Extension of the Shapley-Aumann-Myerson
Solution and Misleading Policy Implications
As of Nieva (October 2002, June 2003) most games on
foundations of institutions, yield empty cores provided that
the value of the two identical player coalition in a third
party enforcer game is high enough relative to the value of
the grand coalition. We propose an extension of the
Aumann-Myerson solution in which pairs of players not only
propose links but propose payoffs constrained on the sum of
the Myerson values of the graph implied by the prospective
link. Partial results point out to the not formation of the
grand coalition, whenever the core is empty in contrast to
the standard solution. The latter would point out instead to
a Coasian postulate of efficiency and it would be more
informative to talk about institutions that are not agreed
upon. With respect to the Coase invariance theorem, we give
a counterexample in which allowing for externalities in
coalition formation induces the grand coalition to form.
This contrasts with Aviazan and Callen original example in
which two firms pollute unilaterally a third one. In our
case, we have a second source of externality that induces a
lower payoff to the pollutee when the two polluters collude.
However, we point out that allowing for nontrasferable
utilities will yield robustness of Hurwicz's (1999) result:
That in two person games, zero income effects or parallel
preferences are necessary and sufficient for different
allocation of pollution rights to influence the level of
pollution. Finally, we dicuss misleading policy
implications.
Talk time: Friday 25 July,
10:50-11:15 Paper with full author
list: coajpet1.pdf (226 kB)
62 Ricardo
Nieva: Enforcers and Induced Empty Core Games Derived From
Any TU 2-Person Game: Ineffective Implementation or Not Agreed Upon
Institutions?
We add a Principal (abstract enforcer) to any 2 person TU
game in strategic form because of transaction costs or
extorsion. The game yields in reasonable cases an empty
core when there are no externalities in coalition formation
and when the principal can choose any allocation on the
frontier of the individual, rational and feasible set. The
principal does so by inducing "The Simultaneous and Double
Extorsion Game". Only one of the identical players and the
principal collude, iff the identical agents combined "might"
is more than a threshold of the principal's but less than
100%, i.e."divide and rule". The threshold depends on the
limit to the degree of double extorsion. Strikingly, he
would prefer to induce an empty core game with an extreme
level of extortion instead of a nonempty core one. The
result, ie. that only an identical agent and the principal
collude, is robust to allowing for variable principal
"might" or harrasing ability that might induce a cooperative
game with externalities in coalition formation. As solution
concept, we use an extension of Myerson's (1978) Shapley
value generalization to partition function games and the
Aumann-Myerson link (1988) formation game.
Talk time: Wednesday 23 July,
10:15-10:40 Paper with full author
list: interaer1.pdf
(277 kB, revised July 20)
63 Ipek
Ozkal-Sanver: Nash Implementation via Hyperfunctions
Hyperfunctions are social choice rules which assign sets of
alternatives to preference profiles over sets. So, they are
more general objects compared to standard (social choice)
correspondences. Thus every correspondence can be expressed
in terms of an equivalent hyperfunction. We postulate the
equivalence between implementing a correspondence and its
equivalent hyperfunction. We give a partial charaterization
of Nash implementable hyperfunctions and explore the
conditions under which correspondences have Nash
implementable equivalent hyperfunctions. Depending on the
axioms used to extend preferences over alternatives to sets,
these conditions are weaker than or logically independent of
Maskin monotonicity, in any case expanding the set of Nash
implementable social choice rules. In fact, social choice
rules such as the majority rule and the top cycle are Nash
implementable through their equivalent hyperfunctions while
they are not Maskin monotonic, thus not Nash implementable
in the standard framework.
Talk time: Monday 21 July,
10:15-10:40 Paper with full author
list: hyperfunctions.pdf
(215 kB)
64 T.
Parthasarathy: SER-SIT Stochastic Games and Vertical Linear
Complementarity Problem
In this note, we consider a two-person nonzerosum finite
stochastic game with SER-SIT properties, that is, with
separable rewards and state independent transitions. We
formulate the given problem as a vertical linear
complementarity problem for the discounted and the
undiscounted stochastic games. Our result generalizes an
earlier result obtrained by Parthasarthy, Tijs and Vrieze.
Talk time: Friday 25 July,
10:50-11:15 Paper with full author
list: ssgv.pdf (157 kB)
65 Yohan
Pelosse: Anonymous Competitive Contracts
In this paper we consider a situation in which a principal
wants to reward the most productive of two agents competing
over T periods while, at the same time eliciting a maximal
effort level from them. Dubey and Wu (2000) and Dubey and
Haimanko (2000) have shown that these two objectives cannot
be satisfied simultaneously. Basically this arises because
one of the agents may have a considerable lead over his
rival at an interim period. For this reason, these authors
advocate the use of a spot-check device so as to provide the
correct incentives to the agents. However, such a mechanism
suffers from a limitation because of its inability to select
the biggest producer of the competition. In this paper, we
show that there exists a more general mechanism that
achieves the two objectives simultaneously. Our analysis is
based on a function that assigns to every possible
difference in the agents' output a probabitity of winning
the prize. We provide a characterization of this optimal
function and study its different properties.
Talk time: Monday 21 July,
10:50-11:15 Paper with full author
list: acc3.pdf (290 kB)
67 Anders
Poulsen: Evolution of Preferences in a Simple Game of Life
We study the evolution of preferences when players are
engaged in simultaneous and sequential move Prisoner's
Dilemma games. There is, as long as each game is played
with strictly positive probability, a unique asymptotically
stable population where players with reciprocal, altruist
and materialist preferences co-exist in the population.
Talk time: Monday 21 July,
3:35-4:00 Paper with full author
list: evol.pdf
(455 kB, revised July 16)
69 Indrajit
Ray: Observable Implications of Nash and Subgame-Perfect
Behavior in Extensive Games
We provide necessary and sufficient conditions for observed
outcomes in extensive game forms to be rationalised first,
partially, as a Nash equilibrium and then, fully, as the
unique subgame perfect equilibrium.
Talk time: Tuesday 22 July,
10:50-11:15 Paper with full author
list: rationalisation.pdf
(159 kB)
In this work we consider cost games in characteristic
function form where the players are not homogenous. It is
supposed that each player is formed by a number of
indistinguishable agents. We determined tariffs for the
agents in such a way the amount is gathered coincide with
the cost of give service to the gran coalition. The tariffs
are determined supposing additivity and the principle of
decomposition using the canonical dual base of the space of
cooperative games.
Talk time: Wednesday 23 July,
10:15-10:40 Paper with full author
list: Sanchez.pdf (103 kB)
73 M. Remzi
Sanver: Almost all Social Choice Correspondences are Subject
to the Gibbard-Satterthwaite Theorem
We analyse the manipulability of social choice
correspondences via hyperfunctions, i.e., functions that
pick a non-empty set of alternatives at each admissible
preference profile over sets of alternatives. We consider a
domain of lexicographic orderings of sets which allows only
two orderings for every ordering over alternatives. We show
that Gibbard-Satterthwaite type impossibility results
prevail on this very narrow domain which is a subset of many
restricted domains defined through standard axioms to extend
preferences over alternatives to sets of alternatives.
Hence, we are able to verify the robustness of the
Gibbard-Satterthwaite theorem, showing that it holds under
almost all reasonable domain restrictions. As hyperfunctions
are more general objects than regular social choice
correspondences, our impossibility results carry to the
standard framework.
Talk time: Monday 21 July,
10:50-11:15 Paper with full author
list: ozyurtsanver.pdf (298 kB)
The Lemke-Howson algorithm is the main algorithm for finding
one equilibrium of a bimatrix game. In this paper we
present a class of square bimatrix games for which the
shortest Lemke-Howson path grows exponentially in the
dimension of the game d. We construct the games using pairs
of dual cyclic polytopes with 2d facets in d-space.
Talk time: Tuesday 22 July,
3:00-3:25 Paper with full author
list: savani.txt (1 kB)
76 Jochen
Schanz: Optimal Information Disclosure for a Policymaker
Targeting Aggregate Activity
This paper starts from the stylised fact that policymakers
publish their information only selectively: a central bank
tends not to predict a recession and the IMF is unlikely to
forecast a currency crisis. The paper, then, searches for
the circumstances in which such a partially-revealing
reporting rule is part of an (sequential) equilibrium within
a static signalling game in which market participants (the
receivers) take the policymaker's reporting strategy into
account when evaluating his report. The economic framework
is a partial equilibrium model of an imperfectly competitive
economy with uncertain demand. To circumvent full
revelation, it is assumed that the policymaker fears that
markets would overreact to such information if it were
published. Results available so far suggest that the
equilibrium reporting rule has the following properties:
extreme news is withheld and intermediate news published. In
addition, the higher the policymaker's incentive to increase
production (i.e., the less competitive the economy is), the
worse the worst news he makes public; likewise, the better
the best news he makes public; the lower the market's
expectation of his information if he withholds; and the
better the average news he publishes.
Talk time: Thursday 24 July,
3:35-4:00 Paper with full author
list: Schanzabstract.pdf
(280 kB, revised July 9)
Standard state-space models, which are widely used in
economics, preclude non-trivial forms of unawareness as
shown by Dekel, Lipman and Rustichini (1998). We define a
generalized state-space model that allows for unawareness.
In order to facilitate applications we make no explicit use
of modal syntax within the sematic model. Our model
satisfies all "S4" properties as well as all desiderata on
unawareness proposed by Modica and Rustichini (1999),
Halpern (2001) as well as Dekel, Lipman and Rustichini
(1998).
Talk time: Friday 25 July,
10:50-11:15 Paper with full author
list: heifetzmeierschipper.pdf
(129 kB, revised May 23)
78 Karl
Schlag: On the Value of Randomizing and Limiting Memory in
Repeated Decision-Making Under Minimal Regret
We search for behavioral rules that attain minimax regret
under geometric discounting in the context of repeated
decision making in a stationary environment where payoffs
belong to a given bounded interval. Rules that attain
minimax regret exist and are optimal for Bayesian decision
making under the prior where learning can be argued to be
most difficult. Minimax regret can be attained by
randomizing using a linear function of the previous payoffs.
For myopic individuals, minimax regret behavior requires
only one round of memory, for intermediate discount factors
two rounds of memory suffice to attain minimax regret.
Talk time: Wednesday 23 July,
10:50-11:15 Paper with full author
list: regret4.pdf (290 kB)
79 Tadashi
Sekiguchi: Repeated Games with Observation Costs
This paper analyzes repeated games in which it is possible
for players to observe the other players' past actions
without noise but it is costly. One's observation decision
itself is not observable to the other players, and this
private nature of monitoring activity makes it difficult to
give the players proper incentives to monitor each other. We
provide a sufficient condition for a feasible payoff vector
to be approximated by a sequential equilibrium when the
observation costs are sufficiently small. We then show that
this result generates an approximate Folk Theorem for a wide
class of repeated games with observation costs. The Folk
Theorem holds for a variant of prisoners' dilemma,
partnership games, and any games in which the players have
an ability to "burn" small amounts of their own payoffs.
Talk time: Monday 21 July,
10:50-11:15 Paper with full author
list: obscostWP.pdf (254 kB)
80 Abhijit
Sengupta: Sealed Bid Second Price Auctions with Discrete
Bidding
We analyze a sealed bid second price auction in a framework
in which acceptable bids are restricted to a set of discrete
values. It is assumed throughout that bidder valuations are
independently drawn from a common continuous distribution.
When bidder valuations are uniformly distributed, it is
shown that there exists a unique symmetric pure strategy
equilibrium characterizing bidder behavior. When following
this strategy, bidders may choose to bid strictly above or
strictly below their own valuation. Under such a selling
mechanism allocative efficiency may be sacrificed, in that
with strictly positive probability the item will be awarded
to a bidder other than the bidder with the highest
valuation. By way of example it is shown that, when choosing
the values of an exogenously determined number of discrete
bid levels, a revenue maximizing seller may wish to choose a
level for the highest acceptable bid either strictly greater
than, strictly less than, or exactly equal to the highest
possible bidder valuation. Because of the complexity of the
payoff functions of the bidders, it is not possible to
specify bidder behavior in general. As a result, a numerical
analysis is conducted, assuming that the acceptable bid
levels are "evenly spaced" (that is, assuming that the
distance between any two consecutive bids is equal to t).
Based upon the results of this numerical analysis, it
appears as if the expected revenue of the seller will
increase as t becomes smaller (that is, as the acceptable
bid points become closer to each other). However, the
probability with which the item will be awarded to a bidder
other than the bidder with the highest valuation does not
always diminish as t is made smaller.
Talk time: Monday 21 July,
3:00-3:25 Paper with full author
list: MathewsAbstract1.pdf
(59 kB)
82 Rafael
Tenorio: The Impact of Individual and Group Characteristics
on Strategies and Outcomes in Coordination Games: Theory and Evidence
We analyze the impact of individual and group attributes on
successful play in two types of coordination games or tasks.
In the first game, the likelihood of coordination depends
positively on the homogeneity of group members. The
converse is true in the second game (i.e., heterogeneous
players tend to coordinate more successfully). The players
involved in these games potentially differ in attributes
such as age, gender, or cultural background. We model these
potential differences as "frames" or underlying common
factors, which will influence the group's ability to
coordinate on salient solutions or "focal points." We then
use data from the television game show "Family Feud" to
evaluate the relative importance of alternative frames on
the ability of groups (families) to succeed at these types
of coordination games. We find that group and task
characteristics are more important determinants of
successful coordination than individual characteristics.
Talk time: Thursday 24 July,
3:35-4:00 Paper with full author
list: StonyBrookprop03.pdf
(100 kB)
This paper addresses the following issue: If a set of agents
bargain on a set of feasible alternatives 'under the shadow'
of a voting rule, that is, any agreement can be enforced if
a 'winning coalition' supports it, which general agreements
are likely to arise? In other terms: Which is the influence
that the voting rule used to settle agreements can project
on the outcome? To give an answer we model the situation as
an extension of Nash bargaining problem in which an
arbitrary voting rule replaces the unanimity to settle
agreements by n players. This provides a setting in which a
natural extension of Nash's solution (consistent with
Shapley's value) is obtained axiomatically by, basically,
integrating into a single system Nash's and Shapley's
characterizing systems.
Talk time: Friday 25 July,
10:15-10:40 Paper with full author
list: bvv.pdf (164 kB)
84 Juan
Vidal-Puga: Forming Societies and the Shapley NTU Value
We design a simple protocol of coalition formation. A
society grows up by sequentially incorporating new members.
The negotiations are always bilateral. We study this
protocol in the context of NTU games in characteristic
function form. When the corresponding NTU game (N,V)
satisfies that V(N) is flat, the only payoff which arises in
equilibrium is the Shapley (1969) NTU value.
Talk time: Tuesday 22 July,
3:35-4:00 Paper with full author
list: shapley-ntu6.pdf (299 kB)
Dual reduction, introduced by Myerson, allows to reduce
games in a way that selects among correlated equilibrium
distributions. Myerson's results are first recalled, then
new properties of dual reduction are established. We show
that generic two-player games have a unique sequence of
iterative full dual reductions. We compare dual reduction
to other correlated equilibrium refinements. Finally, we
review and connect the linear programming proofs of
existence of correlated equilibria.
Talk time: Wednesday 23 July,
10:50-11:15 Paper with full author
list: viossat.pdf
(168 kB, revised July 17)
86 Arndt von
Schemde: Construction of Equilibrium Components with
Arbitrary Index and Degree
In this talk we give a brief introduction into the theory of
index and degree of Nash equilibria. After explaining the
general concepts in an informal way, we will, by means
of certain examples, show how Nash equilibrium components of
arbitrary index (or degree) can be constructed. We will then
discuss certain properties of these components and the
question whether the index (or degree) of a component can
be used to capture certain refinement criteria.
Talk time: Thursday 24 July,
3:35-4:00 Paper with full author
list: vonSchemde.pdf
(115 kB, revised July 1)
87 Bernhard von
Stengel: Computationally Efficient Coordination in Game Trees
The solution concept of 'correlated equilibrium' allows
for coordination in games. For game trees with imperfect
information, it gives rise to NP-hard problems, even for
two-player games without chance moves. We introduce the
'extensive form correlated equilibrium' (EFCE), which
extends Aumann's correlated equilibrium, where coordination
is achieved by signals that are received 'locally' at
information sets. An EFCE is polynomial-time computable for
two-player games without chance moves.
Talk time: Wednesday 23 July,
10:15-10:40 Paper with full author
list: EFCE.pdf (87 kB)
88 Jun Wako:
Two Examples in a Market with Two Types of Indivisible Good
We consider an extension of the permutation game of Tijs et
al (1984) in which players are endowed with and ultimately
wish to consume one unit of each of two types of good (i.e.,
a house and a car). We present two examples. The first is a
case where even though the Corresponding Linear Program
(CLP) does not solve with integers, the core of the market
is not empty. The second example is a case with additively
separable preferences in which there is a core vector in the
market which does not correspond to any optimal dual
solution of the CLP. Both examples demonstrate possible
behavior that is impossible in many of the standard matching
games. We show that in cases with additively separable
preferences, the core-optimal dual equivalence property is
recovered if each component swapping game, one with houses
and the other with cars, is ``convex'' in the sense of
Shapley (1971).
Talk time: Tuesday 22 July,
10:50-11:15 Paper with full author
list: WQSB.pdf
(208 kB, revised June 13)
89 Naoki
Watanabe: Asymptotic Properties of the Shapley Value of
Patent Licensing Games
We study the asymptotic properties of the Shapley value of
patent licensing games with the Cournot competition,
shedding light on its relations to the nucleolus, core and
bargaining set. The Shapley value of the outside patentee of
a non-drastic cost-reducing innovaion converges to (a-c),
which coincides with the patentee's profit through
non-cooperative licensing by means of upfront fee (or
royalty) in Kamien and Tauman (1986). The distance between
the asymptotic Shapley value and asymptotic nucleolus
becomes larger as the magnitude of the cost reduction
increases. The limit core is empty, and the asymptotic
Shapley value is excluded from the limit bargaining set. All
the results are based on a new way of deriving a v-function
from n-person games in strategic form.
Talk time: Monday 21 July,
3:00-3:25 Paper with full author
list: Abs-watanabe.pdf (109 kB)
90 David
Wettstein: An Ordinal Shapley Value for Economic Environments
We propose a new solution concept to address the problem of
sharing a surplus among the agents generating it. The
sharing problem is formulated in the preferences-endowments
space. The solution is defined in a recursive manner
incorporating notions of consistency and fairness and
relying on properties satisfied by the Shapley value for
Transferable Utility (TU) games. We show a solution exists,
and refer to it as an Ordinal Shapley value (OSV). The OSV
associates with each problem an allocation as well as a
matrix of concessions "measuring" the gains each agent
foregoes in favor of the other agents. We analyze the
structure of the concessions, and show they are unique and
symmetric. Next we characterize the OSV using the notion of
coalitional dividends, and furthermore show it is monotone
in an agent's initial endowments and satisfies anonymity.
Finally, similarly to the weighted Shapley value for TU
games, we construct a weighted OSV as well.
Talk time: Friday 25 July,
10:50-11:15 Paper with full author
list: osv2.pdf (366 kB)
91 Harald
Wiese: On the Application of an Outside-Option Value to the
Gloves Game
Building on the Shapley value, several partitional values
(or values for coalition structures) have been presented in
the literature, most notably by Aumann and Drčze (1974) (AD
value) and by Owen (1977). A coalition structure is a
partition on the set of players; the sets making up the
partition are called components. The AD value obeys
component efficiency which is a sensible assumption for many
applications. For example, in market games, players that end
up doing business together can be grouped in components and
they share the gains from trade. Also, the power within a
government coalition rests with the parties involved.
However, the AD value does not reflect the fact that the
power of each market participant, or party within the
government, depends on other trade opportunities, or other
governments that might possibly form (outside options). We
therefore develop a new partitional value that is close to
the AD value in obeying component efficiency but does
reflect outside options. In doing so, our value has to
violate the null-player axiom. We apply this value to the
gloves game.
Talk time: Wednesday 23 July,
3:35-4:00 Paper with full author
list: gloves4.pdf
(249 kB, revised July 17)
92 Jun Xue:
Sustaining Cooperation in the Repeated Prisoner's Dilemma with
Local Interaction
This paper studies the repeated prisoner's dilemma in a
local interaction setup. We construct a sequential
equilibrium in pure strategies that sustains cooperation for
sufficiently patient players. The notion of sequential
equilibrium is extended to extensive form games with
infinite time horizon. The strategy is embedded in an
explicitly defined expectation system, which may also be
viewed as a finite state automaton. The belief system is
derived by perturbing the strategy appropriately.
Talk time: Friday 25 July,
10:15-10:40 Paper with full author
list: introductionnew.pdf
(95 kB)
93 Andriy
Zapechelnyuk: Bargaining with a Ruler: Solution
Implementation via Generalized Auction
We consider an n-player bargaining problem, where one
of the players (the ruler) dictates the outcome, and
the others (the agents) negotiate with the ruler to
achieve a desirable outcome and obtain high payoffs.
We consider two (extreme) cases regarding information
about players' payoff functions: Public information
(all payoff functions are publicly known), and private
information (each player knows only his own payoff
function). In the former case, we find a unique
solution to the bargaining problem satisfying certain
axioms (Individual Rationality, Stability, and
Monotonicity), which results that the ruler receives
the highest feasible payoff, while the agents obtain
only their lowest individually rational payoffs. In
the latter case, we also find an axiomatic solution
(satisfying Individual Rationality, Stability, and
Non-manipulability), which results that the ruler
receives the smallest feasible payoff; besides that,
we design a direct mechanism (we call it 'generalized
auction'), which implements it.
Talk time: Monday 21 July,
10:15-10:40 Paper with full author
list: Zapechelnyuk.pdf (89 kB)
In this paper we propose a characterization of the
coalitional value for transferable utility games (Owen,
1977), and we define and study coalitional semivalues, which
are generalizations of semivalues (Dubey, Neyman and Weber,
1981).
Talk time: Thursday 24 July,
10:50-11:15 Paper with full author
list: CS00.pdf (263 kB)
95 Anna
Jaskiewicz: On the Equivalence of Two Expected Average Reward
Criteria for Zero-Sum Semi-Markov Games
In this paper we study two basic optimality criteria used in
the theory of zero-sum semi-Markov games. According to the
first one, the average reward for player 1 is the lim sup of
the expected total rewards over a finite number of jumps
divided by the expected cumulative time of these jumps.
According to the second definition, the average reward (for
player 1) is the lim sup of the expected total rewards over
the finite deterministic horizon divided by the length of
the horizon. We shall call them the ratio-average reward and
time-average reward, respectively. It is known that in
general these two criteria can have nothing to do with each
other. In other words, they may lead to different rewards
and optimal strategies for players. The ratio-average reward
is somewhat easier to study and has been used by many
authors in zero-sum games and in dynamic programming.
Recently, some results concerning the optimality equation
for semi-Markov games with Borel state space and the
ratio-average criterion were given [1]. However, an
equivalence result has not been reported so far for the
Borel (uncountable) state space models. The aim of this
paper is to show the equivalence between two expected
average rewards under some geometric ergodic conditions. At
the same time, we prove that the optimality equations for
the models with these criteria are the same. Our proof is
based on [2] and employs basic facts from renewal theory.
Certain consequences of V-geometric ergodicity given in
enable us to apply the optional sampling theorem of Doob,
which is the core of the proof.
Talk time: Wednesday 23 July,
3:00-3:25 Paper with full author
list: stbr.pdf
(47 kB, revised Apr 23)
96 Wojciech
Polowczuk: On Two-Point Nash Equilibrium in Concave Bimatrix
Games
The concavity of payoff functions is a very often used
assumption, both in theoretical considerations and in
practical applications. The classical result for games on
Rk
with continuous concave payoffs belongs to Nash. However, in
many applications we have not continuous strategy spaces.
More exactly, the decision goods are nondivisible, e.g.
people, cars, shares. In such case we have finitely many
actions and we obtain matrix games. Radzik studied optimal
strategies in zero-sum matrix games with concavity-convexity
properties. He shown that in such games there always exists
a pair of optimal strategies with at most two membered
carriers.
In this paper we generalize the Radzik's results to
two-person non-zero-sum matrix games. The games described by
such payoff matrices well approximate continuous games on
the unit square with payoff functions F1(x, y) concave
in x for each y, and F2(x, y) concave in y for
each x. It is shown, that the optimal strategies in
such games have very simple structure and a search procedure
is given.
Talk time: Wednesday 23 July,
3:00-3:25 Paper with full author
list: Polowczuk.pdf
(49 kB, revised Apr 30)
97 Elina
Eguiazarova: Comparative Statics for the Private Provision of
Public Goods
The theory of voluntary provision of public goods has
received growing attention since the 1950s. A standard
assumption in much of the literature is that public goods
are strictly normal for all consumers at all levels of
wealth. Together with the assumption of strict normality of
private good, it guarantees uniqueness of Nash equilibrium
and has also been proved to be sufficient condition for the
free riding to be exacerbated as the group size increases.
On the other hand, there are interesting examples of
privately provided public good where the assumption of its
strict normality is not justified. We consider the
traditional model of voluntary provision of public goods
with and without imposing the assumption of normality. We
provide a thorough investigation of the effects on optimal
contributions (total and per consumer) and
optimal private consumption of exogenously changing the
number of consumer. The comparative statics analysis
presented in this talk relies on the approach based on
lattice-theoretic methods. We first assume normality of
public good and prove, using the lattice-theoretic
methodology, that the free riding problem becomes worse with
the number of consumer. Then we provide comparative statics
results for the case where the normality assumption is
relaxed and make an attempt to describe the equilibria set.
Talk time: Wednesday 23 July,
10:50-11:15 Paper with full author
list: eg.pdf
(62 kB, revised Apr 30)
98 Giorgos
Stamatopoulos: Innovation and Licensing in Models of Product
Differentiation
In this paper we consider licensing of innovations in
markets with differentiated products. We analyze models
where firms compete in prices and are offered by an outsider
innovator an innovation that increases the quality of their
product. We examine the licensing policies of auction, fixed
fee, linear royalty and their combination; the optimal
number of licensees, the effect of the licensing policies on
the market structure and welfare etc. We then examine the
outcome of a cooperative licensing procedure between the
innovator and the potential licensees where the payoff of
each player is their Shapley value of an appropriately
defined cooperative game.
Talk time: Wednesday 23 July,
10:15-10:40 Paper with full author
list: giorgos.pdf
(41 kB, revised May 11)
99 Guillaume
Lacôte: How to efficiently defeat a strategy of bounded
rationality
In a given finite two-player zero-sum game if player one is
sufficiently bounded in rationality it might be possible for
player two to beat him, i.e. to ensure that he never gets
more than his maxmin payoff in pure strategies at nearly all
stages of the repeated game. The issue in this case is first
to determine the relative minimum bound in complexity
required for player two to defeat player one; it is then to
determine how well player two performs, that is at how many
stages he fails to beat player one and after which stage (if
any) he can be certain to defeat him at each stage.
Elaborating on recent results this paper addresses these
issues in the case where bounded rationality is
alternatively specified by means of finite state automata or
bounded recall strategies.
Talk time: Tuesday 22 July,
10:15-10:40 Paper with full author
list: lacote.pdf
(232 kB, revised May 14)
100 Alexandre
Marino: Continuous Versus Discrete Market Game
De Meyer and Moussa Saley provide an endogenous
justification for the appearance of Brownian Motion in
Finance by modelling the strategic interaction between two
asymmetrically informed market makers with a zero-sum
repeated game with one-sided information. The crucial point
of this justification is the appearance of the normal
distribution in the asymptotic behavior of Vn(P) on the
square root of n. In De Meyer and Moussa Saley's model,
agents can fix a price in a continuous space. In the real
world, the market compels the agents to post prices in a
discrete set. The previous remark raises the following
question: " Does the normal still appear in the asymptotic
analyze for the discrete market game? ". The main topic is
to prove that for all discretization of the set price, Vn(P)
over the square root of n converges uniformly to 0. Despite
of this fact, we don't reject De Meyer, Moussa analysis:
when the size of the discretization step is small as
compared to the square root of n, the continuous market game
is a good approximation of the discrete one.
Talk time: Tuesday 22 July,
10:50-11:15 Paper with full author
list: marino.pdf
(35 kB, revised May 21)
102 Ram
Orzach: Private Information and Nonbinding Arbitration: A
Proposal for Reducing the Costs of Litigation
This paper analyzes a procedure called mediation, that is
really a form o f nonbinding arbitration, applied to cases
filed in U.S. courts. Under the exist ing rules, a party who
rejects an award proposed by the mediator is liable for s
anctions unless the rejection turns out to be justified,
i.e., unless the trial verdict is more favorable to the
rejecting party than the mediation award. This penalty is
designed to induce acceptance of the mediation award by both
parties , in order to minimize the frequency of trial.
We find this procedure to be flawed since it is myopic. It
may be private ly optimal for the parties to mislead the
mediator, with the result that the med iation award deviates
substantially from the claim's true value. This increases
the likelihood the mediation award is rejected, thus
increasing the probability of trial. We propose an
alternative procedure, under which a party would be liab le
for sanctions if, and only if, she deliberately provided
false information to the mediator. In our example each
party has private information, and the media tor must
acquire all his information from the parties. In comparison
to the exi sting practice, our procedure has a lower
frequency of trial, and provides an ex ante gain to both
parties.
Talk time: Tuesday 22 July,
10:50-11:15 Paper with full author
list: introSB.txt
(2 kB, revised June 4)
103 Eran
Shmaya: Two Player Non Zero-sum Stopping Games in Discrete
Time
A two player stopping game is played in stages. At every
stage, each player can stop or continue. If both players
continue, the game moves to the next stage. If one of the
player stops, the game terminates with final payoff that
depends on the stage and the set of players that stopped.
If the game never terminates the final payoff is zero. We
prove that the game admits epsilon-equilibrium in
randomized strategies for every epsilon > 0.
The proof uses Ramsey Theorem in order reduce the problem to
that of studying properties of epsilon-equilibria in a
simple class of stochastic games with finite state space.
We also generalize the necessary corollary of Ramsey Theorem
to a stochastic setup.
Talk time: Tuesday 22 July,
3:35-4:00 Paper with full author
list: shmaya.pdf
(316 kB, revised June 4)
104 Abdel-Hameed
Nawar: Internet Auctions with Traffic Congestion
This paper addresses the issue of timing of bids in a model
of internet auction with traffic congestion. In a recent
paper, Roth and Ockenfels (2002) have proposed a model of
internet auction and have shown that there is an equilibrium
where every player acts only in the last period of the game.
In their model, time is a continuous interval [0, 1)
with a distinct last period t = 1. There are two
players and valuation of each player can take two values:
high or low. In the model of Roth and Ockenfels, there is
traffic congestion only in the last period, i.e., a bid
submitted in the last period is transmitted successfully
with probability p, where 0 < p < 1,
while in any other period, all bids are transmitted with
probability one. The result of Roth and Ockenfels rely on
two key aspects: (i) time before the last period is
continuous, so that there is always time to react to any
bid, and (ii) other players punish a deviating player by
taking the effort of bidding their valuations even though
they have zero probability of earning a positive payoff. In
this paper, we develop a model of internet auction where
time is discrete. Further, we propose a realistic mechanism
of bid transfer by making it dependent on the number of
submitted bids. First, we show that under suitable
assumptions on the bid transfer mechanism, there is a
symmetric subgame-perfect equilibrium where every player
bids his true valuation unless his bid is transmitted or the
current highest bid exceeds his valuation. Then, we make the
following reasonable assumption on the behavior of the
players: no player acts at a node where he has zero
probability of earning a positive payoff. Under this
assumption, it is shown that the equilibrium described above
is in fact the unique symmetric subgame- perfect
equilibrium. Thus, the "last minute bidding" phenomenon of
Roth and Ockenfels is not sustained when we consider a
discrete-time internet auction.
Talk time: Thursday 24 July,
3:00-3:25 Paper with full author
list: nawar.pdf
(43 kB, revised June 16)
105 Debapriya
Sen: General Licensing Schemes for a Cost-Reducing Innovation
Optimal combinations of upfront fee and royalty are
considered for a cost-reducing innovation in a Cournot
oligopoly industry. The consumers are better off, firms are
worse off and welfare is increased due to the innovation.
The post-innovation price and payoff of any firm is higher
with an incumbent innovator. An incumbent innovator sells
the license to every firm except perhaps one. This is true
for an outsider innovator only for less significant
innovations, while for significant innovations, the license
is sold to only two firms and a natural duopoly is created.
The private value of the patent is increasing in the
magnitude of the innovation for both types of innovators.
Compared to an outsider, an incumbent producer has higher
incentives to develop significant innovations if she assigns
a high probability to the event that someone else would
succeed to innovate in case she fails, while the converse
holds if this probability is small. Finally, for significant
innovations, the industry size that provides the highest
incentive to innovate increases in the magnitude of the
innovation.
Talk time: Wednesday 23 July,
10:50-11:15 Paper with full author
list: sentauman.pdf
(248 kB, revised June 16)
106 Rabah
Amir: Merger Performance under Uncertain Efficiency Gains
In view of the uncertainty over the ability of merging firms
to achieve efficiency gains, we model the post-merger
situation as a Cournot oligopoly wherein the outsiders face
uncertainty about the merged entity's final cost. At the
Bayesian equilibrium, a bilateral merger is profitable
provided the non-merged firms sufficiently believe that the
merger will generate large enough efficiency gains, even if
ex post none actually materialize. The eects of the merger
on market performance are shown to follow similar
threshold rules. The findings are broadly consistent with
stylized facts. An extensive welfare analysis is conducted,
bringing out the key role of efficiency gains and the
different implications of consumer and social welfare
standards.
Talk time: Friday 25 July,
10:50-11:15 Paper with full author
list: ADX91.pdf
(641 kB, revised June 27)
107 Oleksii
Birulin: Public Goods with Congestion: A Mechanism Design
Approach
I consider the problem of efficient provision of the public
good with congestion in the setting with asymmetric
information. I show, in particular, that when congestion is
taken into account, in a wide class of economies it is
possible to construct an incentive compatible mechanism that
always produces the good at the efficient level, balances
the budget and satisfies each consumerís voluntary
participation constraint. This result is in contrast with
the corresponding impossibility result for pure public goods
due to Rob (1989) and Mailath and Postlewiate (1990).
Talk time: Thursday 24 July,
10:15-10:40 Paper with full author
list: congestionjuly3.pdf
(294 kB, revised July 2)
Last change:
Wed Dec 10 11:48:13 GMT 2003
by Bernhard von Stengel