Jean-Guy Mailly

IJCAI Conference 2025 Conference Paper

Argument-based Multi-Issue Negotiation

• Thalya Fossey
• Jean-Guy Mailly
• Pavlos Moraitis

Automated negotiation aims at finding agreements between agents with conflicting goals. Existing utility-based approaches guarantee agents satisfaction with negotiation outcomes, especially in multi-issue negotiations where concession mechanisms lead to win-win results. However, they lack explainability and do not consider agents’ beliefs. On the other hand, argument-based approaches provide reasons for accepting or rejecting offers but do not include utility modeling for offers or enable concession mechanisms in multi-issue settings. We propose a novel hybrid approach combining both types of approaches. The utility-based component enables agents to make concessions on complex negotiation objects to achieve win-win outcomes, while the argumentation component ensures that accepted offers align with the agents' personal argumentation theories. These theories represent their beliefs, encoding various profiles, ethical considerations, social norms, or legal principles.

KR Conference 2025 Conference Paper

Counterexample-Guided Abstraction Refinement for Assumption-based Argumentation

• Jean Marie Lagniez
• Emmanuel Lonca
• Jean-Guy Mailly

Assumption-Based Argumentation (ABA) is a prominent formalism for structured argumentation, widely applied in domains such as healthcare, law, and robotics. Despite its inherent computational complexity, ABA has seen the development of effective techniques that successfully address key tasks, including evaluating the acceptability of literals and computing framework extensions. These approaches typically involve translating the initial ABA framework into an intermediate formalism, such as an Answer Set Program or an Abstract Argumentation Framework, which is then encoded into a Boolean satisfiability (SAT) problem. However, this translation can lead to large and complex intermediate representations, posing challenges for state-of-the-art SAT solvers. In this work, we propose a Counterexample-Guided Abstraction Refinement (CEGAR) approach that bypasses the initial translation step, at the cost of incrementally discovering certain ABA constraints that are not explicitly captured in the initial SAT encoding. We analyze the performance of our method and demonstrate that it outperforms state-of-the-art approaches on specific problem classes, while remaining competitive with the best existing solvers more broadly.

NMR Workshop 2025 Conference Paper

Similarity Measures for First-Order Logical Arguments

• Victor David
• Jérôme Delobelle
• Jean-Guy Mailly

Similarity in formal argumentation has recently gained attention due to its significance in problems such as argument aggregation in semantics and enthymeme decoding. While prior work has focused on propositional logic arguments, we extend these approaches to First-Order Logic (FOL) arguments, enabling reasoning based on the similarity of arguments in more complex and realistic contexts. We present a comprehensive framework for FOL argument similarity, including: 1. An extended axiomatic foundation for similarity measures, 2. A parametric model decomposed into four levels to efficiently evaluate structured knowledge, 3. A Tversky-based family of measures to instantiate these concepts, 4. A set of constraints ensuring well-behaved models that satisfy axioms, and 5. We introduce and analyze non-symmetric similarity measures in formal argumentation for the first time.

AAMAS Conference 2024 Conference Paper

A SAT-based Approach for Argumentation Dynamics

• Jean-Marie Lagniez
• Emmanuel Lonca
• Jean-Guy Mailly

In the realm of multi-agent systems, argumentative dialogues for persuasion and negotiation involve autonomous agents exchanging arguments, necessitating continual re-evaluation of argument acceptability. This study introduces a novel approach using modern SAT solving techniques to dynamically reassess the acceptability status of arguments, aligning with various classical semantics. Our method uses the assumption mechanism in SAT solvers, distinguished by minimal assumptions, ensuring practicality.

ECAI Conference 2024 Conference Paper

Explaining the Lack of Locally Envy-Free Allocations

• Aurélie Beynier
• Jean-Guy Mailly
• Nicolas Maudet
• Anaëlle Wilczynski

In fair division, local envy-freeness is a desirable property which has been thoroughly studied in recent years. In this paper, we study explanations which can be given to explain that no allocation of items can satisfy this criterion, in the house allocation setting where agents receive a single item. While Minimal Unsatisfiable Subsets (MUSes) are key concepts to extract explanations, they cannot be used as such: (i) they highly depend on the initial encoding of the problem; (ii) they are flat structures which fall short of capturing the dynamics of explanations; (iii) they typically come in large number and exhibit great diversity. In this paper we provide two SAT encodings of the problem which allow us to extract MUS when instances are unsatisfiable. We build a dynamic graph structure which allows to follow step-by-step the explanation. Finally, we propose several criteria to select MUSes, some of them being based on the MUS structure, while others rely on this original graphical explanation structure. We give theoretical bounds on these metrics, showing that they can vary significantly for some instances. Experimental results on synthetic data complement these results and illustrate the impact of the encodings and the relevance of our metrics to select among the many MUSes.

JAAMAS Journal 2021 Journal Article

Arguing and negotiating using incomplete negotiators profiles

• Yannis Dimopoulos
• Jean-Guy Mailly
• Pavlos Moraitis

Abstract Computational argumentation has taken a predominant place in the modeling of negotiation dialogues over the last years. A competent agent participating in a negotiation process is expected to decide its next move taking into account an, often incomplete, model of its opponent. This work provides a complete computational account of argumentation-based negotiation under incomplete opponent profiles. After the agent identifies its best option, in any state of a negotiation, it looks for suitable arguments that support this option in the theory of its opponent. As the knowledge on the opponent is uncertain, the challenge is to find arguments that, ideally, support the selected option despite the uncertainty. We present a negotiation framework based on these ideas, along with experimental evidence that highlights the advantages of our approach.

FLAP Journal 2021 Journal Article

Enforcement in Formal Argumentation.

• Ringo Baumann
• Sylvie Doutre
• Jean-Guy Mailly
• Johannes P. Wallner

Within argumentation dynamics, a major strand of research is concerned with how changing an argumentation framework affects the acceptability of arguments, and how to modify an argumentation framework in order to guarantee that some arguments have a given acceptance status. In this chapter, we overview the main approaches for enforcement in formal argumentation. We mainly focus on extension enforcement, i.e., on how to modify an argumentation framework to ensure that a given set of arguments becomes (part of) an extension. We present different forms of extension enforcement defined in the literature, as well as several possibility and impossibility results. The question of minimal change is also considered, i.e., what is the minimal number of modifications that must be made to the argumentation framework for enforcing an extension. Computational complexity and algorithms based on a declarative approach are discussed. Finally, we briefly describe several notions that do not directly fit our definition of extension enforcement, but are closely related.

AAMAS Conference 2021 Conference Paper

Probabilistic Control Argumentation Frameworks

• Fabrice Gaignier
• Yannis Dimopoulos
• Jean-Guy Mailly
• Pavlos Moraitis

In this paper we present Probabilistic Control Argumentation Frameworks (PCAFs) that extend classical Control Argumentation Frameworks (CAFs) to take into account probabilistic information in the reasoning process. We show that probabilities can be used to optimally control CAFs that cannot be controlled otherwise. We introduce the notion of controlling power, that represents the probability that a control configuration reaches its target. A computational method based on Monte Carlo simulations for computing the controlling power of control configurations is defined. We experimentally show that PCAFs outperform w. r. t runtime classical CAFs and in a large number of situations they can reach the target with a high probability while the classical CAFs fail.

KR Conference 2020 Conference Paper

Argument, I Choose You! Preferences and Ranking Semantics in Abstract Argumentation

• Jean-Guy Mailly
• Julien Rossit

Preference-based argumentation and ranking semantics are two important research topics in the computational argumentation literature. Surprisingly, no study investigates to what extent preferences over arguments and ranking semantics can interact. This paper fills the gap between the relative priorities that one can express and the evaluation of arguments individual acceptability. More precisely, we propose a natural principle that should be satisfied by a ranking semantics for Preference-based Argumentation Frameworks. We show that although existing semantics do not satisfy this desirable principle, they can be used to define new ranking semantics that exhibit the expected behavior. Finally, we discuss an application of these semantics to the modeling of human reasoning.

AAMAS Conference 2019 Conference Paper

Argumentation-based Negotiation with Incomplete Opponent Profiles

• Yannis Dimopoulos
• Jean-Guy Mailly
• Pavlos Moraitis

Computational argumentation has taken a predominant place in the modeling of negotiation dialogues over the last years. A competent agent participating in a negotiation process is expected to decide its next move taking into account an, often incomplete, model of its opponent. This work provides a complete computational account of argumentation-based negotiation under incomplete opponent profiles. After the agent identifies its best option, in any state of a negotiation, it looks for suitable arguments that support this option in the theory of its opponent. As the knowledge on the opponent is uncertain, the challenge is to find arguments that, ideally, support the selected option despite the uncertainty. We present a negotiation framework based on these ideas, along with experimental evidence that highlights the advantages of our approach.

AAAI Conference 2018 Conference Paper

Control Argumentation Frameworks

• Yannis Dimopoulos
• Jean-Guy Mailly
• Pavlos Moraitis

Dynamics of argumentation is the family of techniques concerned with the evolution of an argumentation framework (AF), for instance to guarantee that a given set of arguments is accepted. This work proposes Control Argumentation Frameworks (CAFs), a new approach that generalizes existing techniques, namely normal extension enforcement, by accommodating the possibility of uncertainty in dynamic scenarios. A CAF is able to deal with situations where the exact set of arguments is unknown and subject to evolution, and the existence (or direction) of some attacks is also unknown. It can be used by an agent to ensure that a set of arguments is part of one (or every) extension whatever the actual set of arguments and attacks. A QBF encoding of reasoning with CAFs provides a computational mechanism for determining whether and how this goal can be reached. We also provide some results concerning soundness and completeness of the proposed encoding as well as complexity issues.

EUMAS Conference 2017 Conference Paper

Comparison Criteria for Argumentation Semantics

• Sylvie Doutre
• Jean-Guy Mailly

Abstract Argumentation reasoning is a way for agents to evaluate a situation. Given a framework made of conflicting arguments, a semantics allows to evaluate the acceptability of the arguments. It may happen that the semantics associated to the framework has to be changed. In order to perform the most suitable change, the current and a potential new semantics have to be compared. Notions of difference measures between semantics have already been proposed, and application cases where they have to be minimized when a change of semantics has to be performed, have been highlighted. This paper develops these notions, it proposes an additional kind of difference measure, and shows application cases where measures may have to be maximized, and combined.

IJCAI Conference 2016 Conference Paper

Distributing Knowledge into Simple Bases

• Adrian Haret
• Jean-Guy Mailly
• Stefan Woltran

Understanding the behavior of belief change operators for fragments of classical logic has received increasing interest over the last years. Results in this direction are mainly concerned with adapting representation theorems. However, fragment-driven belief change also leads to novel research questions. In this paper we propose the concept of belief distribution, which can be understood as the reverse task of merging. More specifically, we are interested in the following question: given an arbitrary knowledge base K and some merging operator Δ , can we find a profile E and a constraint μ , both from a given fragment of classical logic, such that Δ μ (E) yields a result equivalent to K? In other words, we are interested in seeing if K can be distributed into knowledge bases of simpler structure, such that the task of merging allows for a reconstruction of the original knowledge. Our initial results show that merging based on drastic distance allows for an easy distribution of knowledge, while the power of distribution for operators based on Hamming distance relies heavily on the fragment of choice.

KR Conference 2016 Conference Paper

Merging of AbstractArgumentation Frameworks

• Jerome Delobelle
• Adrian Haret
• Sébastien Konieczny
• Jean-Guy Mailly
• Julien Rossit
• Stefan Woltran

2012; Bisquert et al. 2011; 2013; Boella, Kaci, and van der Formalizing dynamics of argumentation has received increasing attention over the last years. While AGMlike representation results for revision of argumentation frameworks (AFs) are now available, similar results for the problem of merging are still missing. In this paper, we close this gap and adapt model-based propositional belief merging to define extension-based merging operators for AFs. We state an axiomatic and a constructive characterization of merging operators through a family of rationality postulates and a representation theorem. Then we exhibit merging operators which satisfy the postulates. In contrast to the case of revision, we observe that obtaining a single framework as result of merging turns out to be a more subtle issue. Finally, we establish links between our new results and previous approaches to merging of AFs, which mainly relied on axioms from Social Choice Theory, but lacked AGM-like representation theorems.

ECAI Conference 2016 Conference Paper

Translation-Based Revision and Merging for Minimal Horn Reasoning

• Gerhard Brewka
• Jean-Guy Mailly
• Stefan Woltran

In this paper we introduce a new approach for revising and merging consistent Horn formulae under minimal model semantics. Our approach is translation-based in the following sense: we generate a propositional encoding capturing both the syntax of the original Horn formulae (the clauses which appear or not in them) and their semantics (their minimal models). We can then use any classical revision or merging operator to perform belief change on the encoding. The resulting propositional theory is then translated back into a Horn formula. We identify some specific operators which guarantee a particular kind of minimal change. A unique feature of our approach is that it allows us to control whether minimality of change primarily relates to the syntax or to the minimal model semantics of the Horn formula. We give an axiomatic characterization of minimal change on the minimal model for this new setting, and we show that some specific translation-based revision and merging operators satisfy our postulates.

IJCAI Conference 2015 Conference Paper

Extension Enforcement in Abstract Argumentation as an Optimization Problem

• Sylvie Coste-Marquis
• S
• eacute; bastien Konieczny
• Jean-Guy Mailly
• Pierre Marquis

Change in abstract argumentation frameworks (AFs) is a very active topic. Especially, the problem of enforcing a set E of arguments, i. e. , ensuring that E is an extension (or a subset of an extension) of a given AF F, has received a particular attention in the recent years. In this paper, we define a new family of enforcement operators, for which enforcement can be achieved by adding new arguments (and attacks) to F (as in previous approaches to enforcement), but also by questioning some attacks (and non-attacks) of F. This family includes previous enforcement operators, but also new ones for which the success of the enforcement operation is guaranteed. We show how the enforcement problem for the operators of the family can be modeled as a pseudo-Boolean optimization problem. Intensive experiments show that the method is practical and that it scales up well.

JELIA Conference 2014 Conference Paper

A Translation-Based Approach for Revision of Argumentation Frameworks

• Sylvie Coste-Marquis
• Sébastien Konieczny
• Jean-Guy Mailly
• Pierre Marquis

Abstract In this paper, we investigate the revision issue for Dung argumentation frameworks. The main idea is that such frameworks can be translated into propositional formulae, allowing the use of propositional revision operators to perform a rational minimal change. Our translation-based approach to revising argumentation frameworks can take advantage of any propositional revision operator ∘. Via a translation, each propositional operator ∘ can be associated with some revision operators ⋆ suited to argumentation frameworks. Some rationality postulates for the ⋆ operators are presented. If the revision formulae are restricted to formulae about acceptance statuses, some ⋆ operators satisfy these postulates provided that the corresponding ∘ operator is AGM.

KR Conference 2014 Conference Paper

On the Revision of Argumentation Systems: Minimal Change of Arguments Statuses

• Sylvie Coste-Marquis
• Sébastien Konieczny
• Jean-Guy Mailly
• Pierre Marquis

n ntr sio Co an Ex p n on io cti ns tra pa Ex n Co In this paper, we investigate the revision of argumentation systems à la Dung. We focus on revision as minimal change of the arguments status. Contrarily to most of the previous works on the topic, the addition of new arguments is not allowed in the revision process, so that the revised system has to be obtained by modifying the attack relation only. We introduce a language of revision formulae which is expressive enough for enabling the representation of complex conditions on the acceptability of arguments in the revised system. We show how AGM belief revision postulates can be translated to the case of argumentation systems. We provide a corresponding representation theorem in terms of minimal change of the arguments statuses. Several distance-based revision operators satisfying the postulates are also pointed out, along with some methods to build revised argumentation systems. We also discuss some computational aspects of those methods. act ion Undetermined Revision Accepted Rejected Revision Figure 1: Gärdenfors’ epistemic transitions does not make sense to study the revision of argumentation systems directly on the attack graph, independently of any semantics. Stated otherwise, the revision of a given argumentation system under two different semantics may easily lead to two different results. For instance, in the case of the argumentation system AF given in Figure 2, we note that under the stable and preferred semantics, d belongs to every extension, whereas d does not belong to any extension in the case of the grounded semantics. So, revising AF in order to accept d does not need any change for the stable or the preferred semantics, but a change is required for the grounded semantics.

IJCAI Conference 2013 Conference Paper

Dynamic of Argumentation Frameworks

• Jean-Guy Mailly