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Cooperation, Knowledge, and Time: Alternatingtime Temporal Epistemic Logic and its Applications
 Copyright 2004 ACM
, 2003
"... Branchingtime temporal logics have proved to be an extraordinarily successful tool in the formal specification and verification of distributed systems. Much of their success stems from the tractability of the model checking problem for the branching time logic ctl, which has made it possible to imp ..."
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Cited by 53 (7 self)
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Branchingtime temporal logics have proved to be an extraordinarily successful tool in the formal specification and verification of distributed systems. Much of their success stems from the tractability of the model checking problem for the branching time logic ctl, which has made it possible to implement tools that allow designers to automatically verify that systems satisfy requirements expressed in ctl. Recently, ctl was generalised by Alur, Henzinger, and Kupferman in a logic known as "Alternatingtime Temporal Logic" (atl). The key insight in atl is that the path quantifiers of ctl could be replaced by "cooperation modalities", of the form where # is a set of agents. The intended interpretation of an atl formula is that the agents # can cooperate to ensure that # holds (equivalently, that # have a winning strategy for #). In this paper, we extend atl with knowledge modalities, of the kind made popular in the work of Fagin, Halpern, Moses, Vardi and colleagues. Combining these knowledge modalities with atl, it becomes possible to express such properties as "group # can cooperate to bring about # i# it is common knowledge in # that #". The resulting logic  Alternatingtime Temporal Epistemic Logic (atel)  shares the tractability of model checking with its atl parent, and is a succinct and expressive language for reasoning about gamelike multiagent systems.
Towards a Logic of Rational Agency
, 2003
"... Rational agents are important objects of study in several research communities, including economics, philosophy, cognitive science, and most recently computer science and artificial intelligence. Crudely, a rational agent is an entity that is capable of acting on its environment, and which chooses t ..."
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Cited by 52 (6 self)
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Rational agents are important objects of study in several research communities, including economics, philosophy, cognitive science, and most recently computer science and artificial intelligence. Crudely, a rational agent is an entity that is capable of acting on its environment, and which chooses to act in such a way as to further its own best interests. There has recently been much interest in the use of mathematical logic for developing formal theories of such agents. Such theories view agents as practical reasoning systems, deciding moment by moment which action to perform nexi, given the beliefs they have about the world and their desires with respect to how they would like the world to be. In this article, we survey the state of the art in developing logical theories of rational agency. Following a discussion on the dimensions along which such theories can vary, we briefly survey the logical tools available in order to construct such theories. We then review and critically assess three of the best known theories of rational agency: Cohen and Levesque's intention logic, Rao and Georgeff's BDI logics, and the KARO framework of Meyer et al. We then discuss the various roles that such logics can play in helping us to engineer rational agents, and conclude with a discussion of open problems.
On the Computational Complexity of Qualitative Coalitional Games
 Artificial Intelligence
, 2004
"... We study coalitional games in which agents are each assumed to have a goal to be achieved, and where the characteristic property of a coalition is a set of choices, with each choice denoting a set of goals that would be achieved if the choice was made. Such qualitative coalitional games (QCGs) are a ..."
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Cited by 46 (15 self)
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We study coalitional games in which agents are each assumed to have a goal to be achieved, and where the characteristic property of a coalition is a set of choices, with each choice denoting a set of goals that would be achieved if the choice was made. Such qualitative coalitional games (QCGs) are a natural tool for modelling goaloriented multiagent systems. After introducing and formally defining QCGs, we systematically formulate fourteen natural decision problems associated with them, and determine the computational complexity of these problems. For example, we formulate a notion of coalitional stability inspired by that of the core from conventional coalitional games, and prove that the problem of showing that the core of a QCG is nonempty is D 1 complete. (As an aside, we present what we believe is the first "natural" problem that is proven to be complete for D 2 .) We conclude by discussing the relationship of our work to other research on coalitional reasoning in multiagent systems, and present some avenues for future research.
On The Logic Of Cooperation And Propositional Control
, 2005
"... Cooperation logics have recently begun to attract attention within the multiagent systems community. Using a cooperation logic, it is possible to represent and reason about the strategic powers of agents and coalitions of agents in gamelike multiagent systems. These powers are generally assumed t ..."
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Cited by 46 (19 self)
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Cooperation logics have recently begun to attract attention within the multiagent systems community. Using a cooperation logic, it is possible to represent and reason about the strategic powers of agents and coalitions of agents in gamelike multiagent systems. These powers are generally assumed to be implicitly defined within the structure of the environment, and their origin is rarely discussed. In this paper, we study a cooperation logic in which agents are each assumed to control a set of propositional variablesthe powers of agents and coalitions then derive from the allocation of propositions to agents. The basic modal constructs in this Coalition Logic of Propositional Control (CLPC) allow us to express the fact that a group of agents can cooperate to bring about a certain state of affairs. After motivating and introducing CLPC, we provide a complete axiom system for the logic, investigate the issue of characterising control in CLPC with respect to the underlying power structures of the logic, and formally investigate the relationship between CLPC and Pauly's Coalition Logic. We then show that the model checking and satisfiability problems for CLPC are both PSPACEcomplete, and conclude by discussing our results and how CLPC sits in relation to other logics of cooperation.
Coalition games and alternating temporal logics
 Proceeding of the Eighth Conference on Theoretical Aspects of Rationality and Knowledge (TARK VIII
, 2001
"... We draw parallels between coalition game logics developed in [Pauly, 2000b] and [Pauly, 2000c] on one hand, and alternatingtime temporal logics of computations introduced in [Alur et al, 97] on the other. In particular, we show equivalence of their semantics, embedding of coalition game logics int ..."
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Cited by 38 (3 self)
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We draw parallels between coalition game logics developed in [Pauly, 2000b] and [Pauly, 2000c] on one hand, and alternatingtime temporal logics of computations introduced in [Alur et al, 97] on the other. In particular, we show equivalence of their semantics, embedding of coalition game logics into alternatingtime temporal logic, and propose axiomatic systems for these logics. 1
Social laws in alternating time: Effectiveness, feasibility, and synthesis
 SYNTHESE
, 2007
"... Since it was first proposed by Moses, Shoham, and Tennenholtz, the social laws paradigm has proved to be one of the most compelling approaches to the offline coordination of multiagent systems. In this paper, we make four key contributions to the theory and practice of social laws in multiagent syst ..."
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Cited by 37 (13 self)
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Since it was first proposed by Moses, Shoham, and Tennenholtz, the social laws paradigm has proved to be one of the most compelling approaches to the offline coordination of multiagent systems. In this paper, we make four key contributions to the theory and practice of social laws in multiagent systems. First, we show that the Alternatingtime Temporal Logic (atl) of Alur, Henzinger, and Kupferman provides an elegant and powerful framework within which to express and understand social laws for multiagent systems. Second, we show that the effectiveness, feasibility, and synthesis problems for social laws may naturally be framed as atl model checking problems, and that as a consequence, existing atl model checkers may be applied to these problems. Third, we show that the complexity of the feasibility problem in our framework is no more complex in the general case than that of the corresponding problem in the Shoham–Tennenholtz framework (it is npcomplete). Finally, we show how our basic framework can easily be extended to permit social laws in which constraints on the legality or otherwise of some action may be explicitly required. We illustrate the concepts and techniques developed by means of a running example.
PSPACE bounds for rank 1 modal logics
 IN LICS’06
, 2006
"... For lack of general algorithmic methods that apply to wide classes of logics, establishing a complexity bound for a given modal logic is often a laborious task. The present work is a step towards a general theory of the complexity of modal logics. Our main result is that all rank1 logics enjoy a sh ..."
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Cited by 26 (15 self)
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For lack of general algorithmic methods that apply to wide classes of logics, establishing a complexity bound for a given modal logic is often a laborious task. The present work is a step towards a general theory of the complexity of modal logics. Our main result is that all rank1 logics enjoy a shallow model property and thus are, under mild assumptions on the format of their axiomatisation, in PSPACE. This leads to a unified derivation of tight PSPACEbounds for a number of logics including K, KD, coalition logic, graded modal logic, majority logic, and probabilistic modal logic. Our generic algorithm moreover finds tableau proofs that witness pleasant prooftheoretic properties including a weak subformula property. This generality is made possible by a coalgebraic semantics, which conveniently abstracts from the details of a given model class and thus allows covering a broad range of logics in a uniform way.
Alternatingtime temporal logics with irrevocable strategies
 In Proceedings of the 11th Conference on Theoretical Aspects of Rationality and Knowledge (TARK’07
"... In Alternatingtime Temporal Logic (atl), one can express statements about the strategic ability of an agent (or a coalition of agents) to achieve a goal φ such as: “agent i can choose a strategy such that, if i follows this strategy then, no matter what other agents do, φ will always be true”. Howe ..."
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Cited by 20 (5 self)
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In Alternatingtime Temporal Logic (atl), one can express statements about the strategic ability of an agent (or a coalition of agents) to achieve a goal φ such as: “agent i can choose a strategy such that, if i follows this strategy then, no matter what other agents do, φ will always be true”. However, strategies in atl are revocable in the sense that in the evaluation of the goal φ the agent i is no longer restricted by the strategy she has chosen in order to reach the state where the goal is evaluated. In this paper we consider alternative variants of atl where strategies, on the contrary, are irrevocable. The difference between revocable and irrevocable strategies shows up when we consider the ability to achieve a goal which, again, involves (nested) strategic ability. Furthermore, unlike in the standard semantics of atl, memory plays an essential role in the semantics based on irrevocable strategies. 1
Modular algorithms for heterogeneous modal logics
 IN AUTOMATA, LANGUAGES AND PROGRAMMING, ICALP 07, VOL. 4596 OF LNCS
, 2007
"... Statebased systems and modal logics for reasoning about them often heterogeneously combine a number of features such as nondeterminism and probabilities. Here, we show that the combination of features can be reflected algorithmically and develop modular decision procedures for heterogeneous modal ..."
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Cited by 16 (11 self)
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Statebased systems and modal logics for reasoning about them often heterogeneously combine a number of features such as nondeterminism and probabilities. Here, we show that the combination of features can be reflected algorithmically and develop modular decision procedures for heterogeneous modal logics. The modularity is achieved by formalising the underlying statebased systems as multisorted coalgebras and associating both a logical and an algorithmic description to a number of basic building blocks. Our main result is that logics arising as combinations of these building blocks can be decided in polynomial space provided that this is the case for the components. By instantiating the general framework to concrete cases, we obtain PSPACE decision procedures for a wide variety of structurally different logics, describing e.g. Segala systems and games with uncertain information.
Rank1 modal logics are coalgebraic
 IN STACS 2007, 24TH ANNUAL SYMPOSIUM ON THEORETICAL ASPECTS OF COMPUTER SCIENCE, PROCEEDINGS
, 2007
"... Coalgebras provide a unifying semantic framework for a wide variety of modal logics. It has previously been shown that the class of coalgebras for an endofunctor can always be axiomatised in rank 1. Here we establish the converse, i.e. every rank 1 modal logic has a sound and strongly complete coal ..."
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Cited by 14 (11 self)
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Coalgebras provide a unifying semantic framework for a wide variety of modal logics. It has previously been shown that the class of coalgebras for an endofunctor can always be axiomatised in rank 1. Here we establish the converse, i.e. every rank 1 modal logic has a sound and strongly complete coalgebraic semantics. As a consequence, recent results on coalgebraic modal logic, in particular generic decision procedures and upper complexity bounds, become applicable to arbitrary rank 1 modal logics, without regard to their semantic status; we thus obtain purely syntactic versions of these results. As an extended example, we apply our framework to recently defined deontic logics.