Abstract. Building on a long research tradition (cf. 1), this paper proposes to apply the distinction between data (information stored in the agent’s mind) and beliefs

Abstract. This paper compares within the MAS framework two separate threads in the formal study of epistemic change: belief revision and argumentation theories. Belief revision describes how an agent is supposed to change his own mind, while argumentation deals with persuasive strategies employed to change the mind of other agents. These are two sides (cognitive and social) of the same epistemic coin: argumentation theories are incomplete, if they cannot be grounded in belief revision models – and vice versa. Nonetheless, so far the formal treatment of belief revision mostly neglected any systematic comparison with argumentation theories. In MAS such problem becomes evident and inescapable: belief change is usually triggered by communication and persuasion from other agents, involving deception, trust, reputation, negotiation, conflict resolution (all typical issues faced by argumentation-based models). Therefore, a closer comparison between belief revision and argumentation is a necessary preliminary step towards an integrated model of epistemic change in MAS.

www.elsevier.com/locate/artint Since belief revision deals with the interaction of belief and information over time, branching-time temporal logic seems a natural setting for a theory of belief change. We propose two extensions of a modal logic that, besides the next-time temporal operator, contains a belief operator and an information operator. The first logic is shown to provide an axiomatic characterization of the first six postulates of the AGM theory of belief revision, while the second, stronger, logic provides an axiomatic characterization of the full set of AGM postulates.

Introduction Imagine three players Anne, Bill, and Cath, each holding one card from a `stack' of three (known) cards clubs, hearts, and spades, such that they only know their own card but do not know which other card is held by which other player. Assume that the actual deal is that Anne holds clubs, Bill holds hearts and Cath holds spades. Now Anne announces that she does not have hearts. What was known before this announcement, and how does this knowledge change as a result of that action? Before, Cath did not know that Anne holds clubs, but afterwards she knows that Anne holds clubs. This is because Cath can reason as follows: "I have spades, so Anne must have clubs or hearts. If she says that she does not have hearts, she must therefore have clubs." Bill knows that Cath now knows Anne's card, even though he does not know himself what Anne's card is. Both before and after, players know which card they hold in their hands. Note that the only change that appears to have taken place i

Abstract. In this work we continue the work initiated in [1], in which a logic of individual and collective acceptance was introduced. Our aim in this paper is to investigate the extension of the logic of acceptance by public announcements of formulas. The function of public announcements is to diminish the space of possible worlds accepted by agents and sets of agents while functioning as members of a given group, team, organization, institution, etc., x. If a set of agents C ends up with an empty set of worlds that they accept while functioning as members of x, then the agents in C do not identify themselves any longer with x. In such a situation the agents in C should have the possibility to join x again. To that aim we discuss at the end of the paper an operation which consists of an agent (or set of agents) joining a given group, team, organization, institution, etc. 1

We contrast Bonanno’s ‘Belief Revision in a Temporal Framework ’ [15] with preference change and belief revision from the perspective of dynamic epistemic logic (DEL). For that, we extend the logic of communication and change of [11] with relational substitutions [8] for preference change, and show that this does not alter its properties. Next we move to a more constrained context where belief and knowledge can be defined from preferences [29; 14; 5; 7], prove completeness of a very expressive logic of belief revision, and define a mechanism for updating belief revision models using a combination of action priority update [7] and preference substitution [8]. 1 Reconstructing AGM Style Belief Revision Bonanno’s paper offers a rational reconstruction of Alchourrón Gärdenfors Makinson style belief revision (AGM belief revision) [1] (see also [22] and [23]), in a framework where modalities B for single agent belief and I for

www.irit.fr/recherches/LILAC, www.irit.fr/recherches/RPDMP

Since Jan Plaza’s public announcement logic PAL [6], logics mixing epistemic and dynamic logic became more and more popular. They have been studied under the denomination dynamic epistemic logics (DEL). One of the parameters of DELs is the kind of epistemic operator that is considered, ranking from individual to common knowledge. Most DELs restrict their attention to the concept of knowledge, and do not consider that of belief. The reason is that an agent’s knowledge has the advantage of being correct: there is no need to revise it. On the contrary, the beliefs entertained by an agent might be erroneous. Upon learning that the agent has to revise his beliefs. A complete account of action and belief requires therefore the inclusion of belief revision mechanisms. The need for such mechanisms is particularly obvious in Alexandru Baltag et col.’s influential generalization of PAL [3, 2] and variants thereof, where events are no longer public, but may be perceived incompletely or erroneously by the different agents: erroneous perception of the (truthful) announcement of p as the announcement

The problem of how to extend epistemic logic (EL) in order to allow for reasoning about knowledge and belief in dynamic contexts gained increasing attention during the last 30 years in the fields of artificial intelligence, theoretical computer science and philosophical logic. EL is a branch of modal logic that was designed in the 60ies by Hintikka in order to study reasoning about knowledge and belief. It allows to model static situations, where we do not have to reason about what holds at different points of time, or about both what holds before and after an event or action. Several approaches were explored to ‘make EL walk’, depending on the field. First, theoretical computer science people mainly worked on combinations of EL and linear-time temporal logic. They proposed a model based on runs (complete sequences of states) and epistemic accessibility relations between runs. They identified the main dichotomies concerning the interaction between knowledge and time, such as: synchronous vs. asynchronous time; perfect recall or no; partial vs. full observability; etc. A complete account of the state of the art

Building on a simple modal logic of context, the paper presents a dynamic logic characterizing operations of contraction and expansion on theories. We investigate the mathematical properties of the logic, and use it to develop an axiomatic and semantic analysis of norm change in normative systems. The proposed analysis advances the state of the art by providing a formal semantics of norm-change which, at the same time, takes into account several different aspects of the phenomenon, such as permission and obligation dynamics, as well as the dynamics of classificatory rules. 1