Davide Grossi

AAAI Conference 2026 Conference Paper

A Fortiori Case-Based Reasoning: From Theory to Data (Abstract Reprint)

• Wijnand van Woerkom
• Davide Grossi
• Henry Prakken
• Bart Verheij

The widespread application of uninterpretable machine learning systems for sensitive purposes has spurred research into elucidating the decision-making process of these systems. These efforts have their background in many different disciplines, one of which is the field of AI & law. In particular, recent works have observed that machine learning training data can be interpreted as legal cases. Under this interpretation, the formalism developed to study case law, called the theory of precedential constraint, can be used to analyze the way in which machine learning systems draw on training data—or should draw on them—to make decisions. In the present work, we advance the theory underlying these explanation methods, by relating it to order theory and logic. This allows us to write a software implementation of the theory that can be used to compute with the definitions and give automatic proofs of the properties of the model. We use this implementation to evaluate the model on a series of datasets. Through this analysis, we characterize the types of datasets that are more, or less, suitable to be described by the theory.

AILAW Journal 2026 Journal Article

Hierarchical models of precedential constraint

• Wijnand van Woerkom
• Davide Grossi
• Henry Prakken
• Bart Verheij

Abstract In recent years, models of a fortiori argumentation from the field of artificial intelligence and law, developed to describe legal case-based reasoning based on precedent, have been successfully applied to improve interpretability of data-driven decision systems. To aid with these applications, we further develop the theory of a fortiori case-based reasoning by extending the knowledge representations on which these models operate. More specifically, we modify the representations to accommodate incomplete information, as well as to incorporate both dimensional (as opposed to binary) and hierarchical (as opposed to unstructured) information. This results in four models—one for each combination of accommodating dimensional or hierarchical information. We investigate their formal properties, and find they are monotonic with respect to the addition of new precedents and of new facts, and that some are conservative extensions of other models. In addition, we exemplify each through a running example from the penitentiary law domain.

JAAMAS Journal 2025 Journal Article

On the graph theory of majority illusions: theoretical results and computational experiments

• Maaike Venema-Los
• Zoé Christoff
• Davide Grossi

Abstract The popularity of an opinion in one’s direct circles is not necessarily a good indicator of its popularity in one’s entire community. Network structures make local information about global properties of the group potentially inaccurate, and the way a social network is wired constrains what kind of information distortion can actually occur. In this paper, we discuss which classes of networks allow for a large enough proportion of the population to get a wrong enough impression about the overall distribution of opinions. We start by focusing on the ‘majority illusion’, the case where one sees a majority opinion in one’s direct circles that differs from the global majority. We show that no network structure can guarantee that most agents see the correct majority. We then perform computational experiments to study the likelihood of majority illusions in different classes of networks. Finally, we generalize to other types of illusions.

JAIR Journal 2024 Journal Article

A Fortiori Case-Based Reasoning: From Theory to Data

• Wijnand van Woerkom
• Davide Grossi
• Henry Prakken
• Bart Verheij

The widespread application of uninterpretable machine learning systems for sensitive purposes has spurred research into elucidating the decision-making process of these systems. These efforts have their background in many different disciplines, one of which is the field of AI & law. In particular, recent works have observed that machine learning training data can be interpreted as legal cases. Under this interpretation, the formalism developed to study case law, called the theory of precedential constraint, can be used to analyze the way in which machine learning systems draw on training data—or should draw on them—to make decisions. In the present work, we advance the theory underlying these explanation methods, by relating it to order theory and logic. This allows us to write a software implementation of the theory that can be used to compute with the definitions and give automatic proofs of the properties of the model. We use this implementation to evaluate the model on a series of datasets. Through this analysis, we characterize the types of datasets that are more, or less, suitable to be described by the theory.

AAMAS Conference 2024 Conference Paper

Emergent Cooperation under Uncertain Incentive Alignment

• Nicole Orzan
• Erman Acar
• Davide Grossi
• Roxana Rădulescu

Understanding the emergence of cooperation in systems of computational agents is crucial for the development of effective cooperative AI. Interaction among individuals in real-world settings are often sparse and occur within a broad spectrum of incentives, which often are only partially known. In this work, we explore how cooperation can arise among reinforcement learning agents in scenarios characterised by infrequent encounters, and where agents face uncertainty about the alignment of their incentives with those of others. To do so, we train the agents under a wide spectrum of environments ranging from fully competitive, to fully cooperative, to mixed-motives. Under this type of uncertainty we study the effects of mechanisms, such as reputation and intrinsic rewards, that have been proposed in the literature to foster cooperation in mixed-motives environments. Our findings show that uncertainty substantially lowers the agents’ ability to engage in cooperative behaviour, when that would be the best course of action. In this scenario, the use of effective reputation mechanisms and intrinsic rewards boosts the agents’ capability to act nearly-optimally in cooperative environments, while greatly enhancing cooperation in mixed-motive environments as well.

ECAI Conference 2024 Conference Paper

Learning in Multi-Objective Public Goods Games with Non-Linear Utilities

• Nicole Orzan
• Erman Acar
• Davide Grossi
• Patrick Mannion
• Roxana Radulescu

Addressing the question of how to achieve optimal decision-making under risk and uncertainty is crucial for enhancing the capabilities of artificial agents that collaborate with or support humans. In this work, we address this question in the context of Public Goods Games. We study learning in a novel multi-objective version of the Public Goods Game where agents have different risk preferences, by means of multi-objective reinforcement learning. We introduce a parametric non-linear utility function to model risk preferences at the level of individual agents, over the collective and individual reward components of the game. We study the interplay between such preference modelling and environmental uncertainty on the incentive alignment level in the game. We demonstrate how different combinations of individual preferences and environmental uncertainty sustain the emergence of cooperative patterns in non-cooperative environments (i. e. , where competitive strategies are dominant), while others sustain competitive patterns in cooperative environments (i. e. , where cooperative strategies are dominant).

ECAI Conference 2024 Conference Paper

Limited Voting for Better Representation?

• Maaike Venema-Los
• Zoé Christoff
• Davide Grossi

Limited Voting (LV) is an approval-based method for multi-winner elections where all ballots are required to have a same fixed size. While it appears to be used as voting method in corporate governance and has some political applications, to the best of our knowledge, no formal analysis of the rule exists to date. We provide such an analysis here, prompted by a request for advice about this voting rule by a health insurance company in the Netherlands, which uses it to elect its work council. We study conditions under which LV would improve representation over standard approval voting and when it would not. We establish the extent of such an improvement, or lack thereof, both in terms of diversity and proportionality notions. These results help us understand if, and how, LV may be used as a low-effort fix of approval voting in order to enhance representation.

AAMAS Conference 2024 Conference Paper

Toward a Quality Model for Hybrid Intelligence Teams

• Davide Dell'Anna
• Pradeep K. Murukannaiah
• Bernd Dudzik
• Davide Grossi
• Catholijn M. Jonker
• Catharine Oertel
• Pinar Yolum

Hybrid Intelligence (HI) is an emerging paradigm in which artificial intelligence (AI) augments human intelligence. The current literature lacks systematic models that guide the design and evaluation of HI systems. Further, discussions around HI primarily focus on technology, neglecting the holistic human-AI ensemble. In this paper, we take the initial steps toward the development of a quality model for characterizing and evaluating HI systems from a human-AI teams perspective. We conducted a study investigating the adequacy of properties commonly associated with effective human teams to describe HI. Our study, featuring the insights of 50 HI researchers, shows that various human team properties, including boundedness, interdependence, competency, purposefulness, initiative, normativity, and effectiveness, are important for HI systems. Our study also reveals limitations in applying certain human team properties, such as coaching, rewards, and recognition, to HI systems due to the inherent human-AI asymmetry.

EUMAS Conference 2023 Conference Paper

On the Graph Theory of Majority Illusions

• Maaike Venema-Los
• Zoé Christoff
• Davide Grossi

Abstract The popularity of an opinion in one’s direct circles is not necessarily a good indicator of its popularity in one’s entire community. For instance, when confronted with a majority of opposing opinions in one’s circles, one might get the impression that one belong s to a minority. From this perspective, network structure makes local information about global properties of the group potentially inaccurate. However, the way a social network is wired also determines what kind of information distortion can actually occur. In this paper, we discuss which classes of networks allow for a majority of agents to have the wrong impression about what the majority opinion is, that is, to be in a ‘majority illusion’.

IJCAI Conference 2022 Conference Paper

Group Wisdom at a Price: Jury Theorems with Costly Information

• Matteo Michelini
• Adrian Haret
• Davide Grossi

We study epistemic voting on binary issues where voters are characterized by their competence, i. e. , the probability of voting for the correct alternative, and can choose between two actions: voting or abstaining. In our setting voting involves the expenditure of some effort, which is required to achieve the appropriate level of competence, whereas abstention carries no effort. We model this scenario as a game and characterize its equilibria under several variations. Our results show that when agents are aware of everyone's incentives, then the addition of effort may lead to Nash equilibria where wisdom of the crowds is lost. We further show that if agents' awareness of each other is constrained by a social network, the topology of the network may actually mitigate this effect.

IJCAI Conference 2022 Conference Paper

Proportional Budget Allocations: Towards a Systematization

• Maaike Los
• Zoé Christoff
• Davide Grossi

We contribute to the programme of lifting proportionality axioms from the multi-winner voting setting to participatory budgeting. We define novel proportionality axioms for participatory budgeting and test them on known proportionality-driven rules such as Phragmén and Rule X. We investigate logical implications among old and new axioms and provide a systematic overview of proportionality criteria in participatory budgeting.

AIJ Journal 2022 Journal Article

Reasoning about general preference relations

• Davide Grossi
• Wiebe van der Hoek
• Louwe B. Kuijer

AAMAS Conference 2022 Conference Paper

Social Choice Around the Block: On the Computational Social Choice of Blockchain

• Davide Grossi

One of the most innovative aspects of blockchain technology consists in the introduction of an incentive layer to regulate the behavior of distributed protocols. The designer of a blockchain system faces therefore issues that are akin to those relevant for the design of economic mechanisms, and faces them in a computational setting. From this perspective the present paper argues for the importance of computational social choice in blockchain research. It identifies a few challenges at the interface of the two fields that illustrate the strong potential for cross-fertilization between them.

AAMAS Conference 2022 Conference Paper

Tracking Truth by Weighting Proxies in Liquid Democracy

• Yuzhe Zhang
• Davide Grossi

We study wisdom-of-the-crowd effects in liquid democracy on networks where agents are allowed to apportion parts of their voting weight to different proxies. We show that in this setting—unlike in the standard one where voting weight is delegated in full to only one proxy—it becomes possible to construct delegation structures that optimize the truth-tracking ability of the group. Focusing on group accuracy we contrast this centralized solution with the setting in which agents are free to choose their weighted delegations by greedily trying to maximize their own individual accuracy. While equilibria with weighted delegations may be as bad as with standard delegations, they are never worse and may sometimes be better. To gain further insights into this model we experimentally study quantal response delegation strategies on random networks. We observe that weighted delegations can lead, under specific conditions, to higher group accuracy than simple majority voting.

LORI Conference 2021 Conference Paper

How Knowledge Triggers Obligation - A Dynamic Logic of Epistemic Conditional Obligation

• Davide Grossi
• Barteld Kooi
• Xingchi Su
• Rineke Verbrugge

Abstract Obligations can be affected by knowledge. Several approaches exist to formalize knowledge-based obligations, but no formalism has been developed yet to capture the dynamic interaction between knowledge and obligations. We introduce the dynamic extension of an existing logic for knowledge-based obligations here. We motivate the logic by analyzing several scenarios and by showing how it can capture in an original manner several fundamental deontic notions such as absolute, prima facie and all-things-considered obligations. Finally, in the dynamic epistemic logic tradition, we provide reduction axioms for the dynamic operator of the new logic.

AAAI Conference 2021 Conference Paper

Power in Liquid Democracy

• Yuzhe Zhang
• Davide Grossi

The paper develops a theory of power for delegable proxy voting systems. We define a power index able to measure the influence of both voters and delegators. Using this index, which we characterize axiomatically, we extend an earlier game-theoretic model by incorporating power-seeking behavior by agents. We analytically study the existence of pure strategy Nash equilibria in such a model. Finally, by means of simulations, we study the effect of relevant parameters on the emergence of power inequalities in the model.

AAAI Conference 2021 Conference Paper

United for Change: Deliberative Coalition Formation to Change the Status Quo

• Edith Elkind
• Davide Grossi
• Ehud Shapiro
• Nimrod Talmon

We study a setting in which a community wishes to identify a strongly supported proposal from a large space of alternatives, in order to change the status quo. We describe a deliberation process in which agents dynamically form coalitions around proposals that they prefer over the status quo. We formulate conditions on the space of proposals and on the ways in which coalitions are formed that guarantee deliberation to succeed, that is, to terminate by identifying a proposal with the largest possible support. Our results provide theoretical foundations for the analysis of deliberative processes in systems for democratic deliberation support, such as, e. g. , LiquidFeedback or Polis.

KR Conference 2020 Conference Paper

Logics of Preference when There Is No Best

• Davide Grossi
• Wiebe van der Hoek
• Louwe B. Kuijer

Well-behaved preferences (e. g. , total pre-orders) are a cornerstone of several areas in artificial intelligence, from knowledge representation, where preferences typically encode likelihood comparisons, to both game and decision theories, where preferences typically encode utility comparisons. Yet weaker (e. g. , cyclical) structures of comparison have proven important in a number of areas, from argumentation theory to tournaments and social choice theory. In this paper we provide logical foundations for reasoning about this type of preference structures where no obvious best elements may exist. Concretely, we compare and axiomatize a number of ways in which the concepts of maximality and optimality can be generalized in this general class of preferences. We thereby expand the scope of the long-standing tradition of the logical analysis of preference.

LORI Conference 2019 Conference Paper

Bipolar Argumentation Frameworks, Modal Logic and Semantic Paradoxes

• Carlo Proietti
• Davide Grossi
• Sonja Smets
• Fernando R. Velázquez-Quesada

Abstract Bipolar Argumentation Frameworks (BAF) are a natural extension of Dung’s Argumentation Frameworks (AF) where a relation of support between arguments is added to the standard attack relation. Despite their interest, BAF present several difficulties and their semantics are quite complex. This paper provides a definition of semantic concepts for BAF in terms of fixpoints of the functions of neutrality and defense, thus preserving most of the fundamental properties of Dung’s AF. From this angle it becomes easy to show that propositional dynamic logic provides an adequate language to talk about BAF. Finally, we illustrate how this framework allows to encode the structure of the referential discourse involved in semantic paradoxes such as the Liar. It turns out that such paradoxes can be seen as BAF without a stable extension.

AAMAS Conference 2019 Conference Paper

Credulous Acceptability, Poison Games and Modal Logic

• Davide Grossi
• Simon Rey

The Poison Game is a two-player game in which players alternatively move a token on a graph’s nodes and such that one player can influence which edges the other player is able to traverse. It operationalizes the notion of existence of credulously acceptable arguments in an argumentation framework or, equivalently, the existence of non-trivial semi-kernels. We develop a modal logic (poison modal logic, PML) tailored to represent winning positions in such a game, thereby identifying the precise modal reasoning that underlies the notion of credulous acceptability in argumentation. We study model-theoretic and decidability properties of PML, and position it with respect to recently studied logics at the cross-road of modal logic, argumentation, and graph games.

JAIR Journal 2019 Journal Article

Negotiable Votes

• Umberto Grandi
• Davide Grossi
• Paolo Turrini

We study voting games on binary issues, where voters hold an objective over the outcome of the collective decision and are allowed, before the vote takes place, to negotiate their ballots with the other participants. We analyse the voters' rational behaviour in the resulting two-phase game when ballots are aggregated via non-manipulable rules and, more specifically, quota rules. We show under what conditions undesirable equilibria can be removed and desirable ones sustained as a consequence of the pre-vote phase.

AAAI Conference 2019 Conference Paper

On Rational Delegations in Liquid Democracy

• Daan Bloembergen
• Davide Grossi
• Martin Lackner

Liquid democracy is a proxy voting method where proxies are delegable. We propose and study a game-theoretic model of liquid democracy to address the following question: when is it rational for a voter to delegate her vote? We study the existence of pure-strategy Nash equilibria in this model, and how group accuracy is affected by them. We complement these theoretical results by means of agent-based simulations to study the effects of delegations on group’s accuracy on variously structured social networks.

AIJ Journal 2019 Journal Article

On the graded acceptability of arguments in abstract and instantiated argumentation

• Davide Grossi
• Sanjay Modgil

LPAR Conference 2018 Conference Paper

When Are Two Gossips the Same?

• Krzysztof R. Apt
• Davide Grossi
• Wiebe van der Hoek

We provide an in-depth study of the knowledge-theoretic aspects of communication in so-called gossip protocols. Pairs of agents communicate by means of calls in order to spread information—so-called secrets—within the group. Depending on the nature of such calls knowledge spreads in different ways within the group. Systematizing existing literature, we identify 18 different types of communication, and model their epistemic effects through corresponding indistinguishability relations. We then provide a classification of these relations and show its usefulness for an epistemic analysis in presence of different communication types. Finally, we explain how to formalise the assumption that the agents have common knowledge of a distributed epistemic gossip protocol.

TARK Conference 2017 Conference Paper

Binary Voting with Delegable Proxy: An Analysis of Liquid Democracy

• Zoé Christoff
• Davide Grossi

The paper provides an analysis of the voting method known as delegable proxy voting, or liquid democracy. The analysis first positions liquid democracy within the theory of binary aggregation. It then focuses on two issues of the system: the occurrence of delegation cycles; and the effect of delegations on individual rationality when voting on logically interdependent propositions. It finally points to proposals on how the system may be modified in order to address the above issues.

IJCAI Conference 2017 Conference Paper

Non-Determinism and the Dynamics of Knowledge

• Davide Grossi
• Andreas Herzig
• Wiebe van der Hoek
• Christos Moyzes

In this paper we attempt to shed light on the concept of an agent’s knowledge after a non-deterministic action is executed. We start by making a comparison between notions of non-deterministic choice, and between notions of sequential composition, of settings with dynamic and/or epistemic character; namely Propositional Dynamic Logic (PDL), Dynamic Epistemic Logic (DEL), and the more recent logic of Semi-Public Environments (SPE). These logics represent two different approaches for defining the aforementioned actions, and in order to provide unified frameworks that encompass both, we define the logics DELVO (DEL+Vision+Ontic change) and PDLVE (PDL+Vision+Epistemic operators). DELVO is given a sound and complete axiomatisation.

LORI Conference 2017 Conference Paper

Stability in Binary Opinion Diffusion

• Zoé Christoff
• Davide Grossi

Abstract The paper studies the stabilization of the process of diffusion of binary opinions on networks. It first shows how such dynamics can be modeled and studied via techniques from binary aggregation, which directly relate to neighborhood frames. It then characterizes stabilization in terms of such neighborhood structures, and shows how the monotone \(\mu \) -calculus can express relevant properties of them. Finally, it illustrates the scope of these results by applying them to specific diffusion models.

IJCAI Conference 2017 Conference Paper

The Ceteris Paribus Structure of Logics of Game Forms (Extended Abstract)

• Davide Grossi
• Emiliano Lorini
• François Schwarzentruber

We present a simple Ceteris Paribus Logic (CP) and study its relationship with existing logics that deal with the representation of choice and power in games in normal form including atemporal STIT, Coalition Logic of Propositional Control (CL-PC) and Dynamic Logic of Propositional Assignments (DL-PA). Thanks to the polynomial reduction of the satisfiability problem for atemporal STIT in the satisfiability problem for CP, we obtain a complexity result for the latter problem.

TARK Conference 2015 Conference Paper

Epistemic Protocols for Distributed Gossiping

• Krzysztof R. Apt
• Davide Grossi
• Wiebe van der Hoek

Gossip protocols aim at arriving, by means of point-to-point or group communications, at a situation in which all the agents know each other's secrets. We consider distributed gossip protocols which are expressed by means of epistemic logic. We provide an operational semantics of such protocols and set up an appropriate framework to argue about their correctness. Then we analyze specific protocols for complete graphs and for directed rings.

IJCAI Conference 2015 Conference Paper

Equilibrium Refinement through Negotiation in Binary Voting

• Umberto Grandi
• Davide Grossi
• Paolo Turrini

We study voting games on binary issues, where voters might hold an objective over some issues at stake, while willing to strike deals on the remaining ones, and can influence one another’s voting decision before the vote takes place. We analyse voters’ rational behaviour in the resulting two-phase game, showing under what conditions undesirable equilibria can be removed as an effect of the prevote phase.

IJCAI Conference 2015 Conference Paper

Finite Abstractions for the Verification of Epistemic Properties in Open Multi-Agent Systems

• Francesco Belardinelli
• Davide Grossi
• Alessio Lomuscio

We develop a methodology to model and verify open multi-agent systems (OMAS), where agents may join in or leave at run time. Further, we specify properties of interest on OMAS in a variant of firstorder temporal-epistemic logic, whose characterising features include epistemic modalities indexed to individual terms, interpreted on agents appearing at a given state. This formalism notably allows to express group knowledge dynamically. We study the verification problem of these systems and show that, under specific conditions, finite bisimilar abstractions can be obtained.

IJCAI Conference 2015 Conference Paper

Formal Analysis of Dialogues on Infinite Argumentation Frameworks

• Francesco Belardinelli
• Davide Grossi
• Nicolas Maudet

The paper analyses multi-agent strategic dialogues on possibly infinite argumentation frameworks. We develop a formal model for representing such dialogues, and introduce FOA-ATL, a first-order extension of alternating-time logic, for expressing the interplay of strategic and argumentation-theoretic properties. This setting is investigated with respect to the model checking problem, by means of a suitable notion of bisimulation. This notion of bisimulation is also used to shed light on how static properties of argumentation frameworks influence their dynamic behaviour.

IJCAI Conference 2015 Conference Paper

On the Graded Acceptability of Arguments

• Davide Grossi
• Sanjay Modgil

The paper develops a formal theory of the degree of justification of arguments, which relies solely on the structure of an argumentation framework. The theory is based on a generalisation of Dung’s notion of acceptability, making it sensitive to the numbers of attacks and counter-attacks on arguments. Graded generalisations of argumentation semantics are then obtained and studied. The theory is applied by showing how it can arbitrate between competing preferred extensions and how it captures a specific form of accrual in instantiated argumentation.

LORI Conference 2015 Conference Paper

Sabotage Modal Logic: Some Model and Proof Theoretic Aspects

• Guillaume Aucher
• Johan van Benthem
• Davide Grossi

Abstract We investigate some model and proof theoretic aspects of sabotage modal logic. The first contribution is to prove a characterization theorem for sabotage modal logic as the fragment of first-order logic which is invariant with respect to a suitably defined notion of bisimulation (called sabotage bisimulation). The second contribution is to provide a sound and complete tableau method for sabotage modal logic. We also chart a number of open research questions concerning sabotage modal logic, aiming at integrating it within the current landscape of logics of model update.

JAIR Journal 2015 Journal Article

The Ceteris Paribus Structure of Logics of Game Forms

• Davide Grossi
• Emiliano Lorini
• Francois Schwarzentruber

The article introduces a ceteris paribus modal logic, called CP, interpreted on the equivalence classes induced by finite sets of propositional atoms. This logic is studied and then used to embed three logics of strategic interaction, namely atemporal STIT, the coalition logic of propositional control (CL−PC) and the starless fragment of the dynamic logic of propositional assignments (DL−PA). The embeddings highlight a common ceteris paribus structure underpinning the key operators of all these apparently very different logics and show, we argue, remarkable similarities behind some of the most influential formalisms for reasoning about strategic interaction

EUMAS Conference 2014 Conference Paper

A Framework for Epistemic Gossip Protocols

• Maduka Attamah
• Hans van Ditmarsch
• Davide Grossi
• Wiebe van der Hoek

Abstract We implement a framework to evaluate epistemic gossip protocols. Gossip protocols spread information within a network of agents by pairwise communications. This tool, Epistemic Gossip Protocol (EGP), is applied to epistemic gossip protocols presented in [ 1 ]. We introduce a programming language for epistemic gossip protocols. We describe an interpreter for this language, together with a model generator and model checker, for a dynamic model of the protocol. The tool EGP outputs key dynamic properties of such protocols, thus facilitating the process of protocol design and planning. We conclude with some experimental results.

KR Conference 2014 Conference Paper

Justified Beliefs by Justified Arguments

• Davide Grossi
• Wiebe van der Hoek

logic and argumentation theory. We hope that the results presented can foster further interaction between the two fields. The paper addresses how the information state of an agent relates to the arguments that the agent endorses. Information states are modeled in doxastic logic and arguments by recasting abstract argumentation theory in a modal logic format. The two perspectives are combined by an application of the theory of product logics, delivering sound and complete systems in which the interaction of arguments and beliefs is investigated. 1 Related work To the best of our knowledge, the only works to date attempting to interface argumentation with epistemic logic are (Grossi 2012) and (Schwarzentruber et al. 2012). The first is concerned with the analysis, in dynamic epistemic logic (van Ditmarsch et al. 2007), of the fixpoint behavior of some argumentation theoretic notions, and the second enriches the standard framework of abstract argumentation by enabling arguers to hold beliefs about other arguers’ available arguments. In its broad purposes, the present paper can be related to recent work (in particular, (Artemov 2008; van Benthem and Pacuit 2011)) aiming at explicitly modeling the ‘justifications’ or ‘reasons’ upon which agents base their information state. Our paper shows the viability of using product logics for this type of analysis.

ECAI Conference 2014 Conference Paper

Knowledge and Gossip

• Maduka Attamah
• Hans van Ditmarsch
• Davide Grossi
• Wiebe van der Hoek

A well-studied phenomenon in network theory are optimal schedules to distribute information by one-to-one communication between nodes. One can take these communicative actions to be 'telephone calls', and this process of spreading information is known as gossiping [4]. It is typical to assume a global scheduler who simply executes a possibly non-deterministic protocol. Such a protocol can be seen as consisting of a sequence of instructions "first, agent a calls b, then c, next, d calls b. .. ". We investigate epistemic gossip protocols, where an agent a will call another agent not because it is so instructed but based on its knowledge or ignorance of the factual information that is distributed over the network. Such protocols therefore don't need a central schedular, but they come at a cost: they may take longer to terminate than non-epistemic, globally scheduled, protocols. We describe various epistemic protocols, we give their logical properties, and we model them in a number of ways.

IJCAI Conference 2013 Conference Paper

Audience-Based Uncertainty in Abstract Argument Games

• Davide Grossi
• Wiebe van der Hoek

The paper generalizes abstract argument games to cope with cases where proponent and opponent argue in front of an audience whose type is known only with uncertainty. The generalization, which makes use of basic tools from probability theory, is motivated by several examples and delivers a class of abstract argument games whose adequacy is proven robust against uncertainty.

TARK Conference 2013 Conference Paper

Ceteris Paribus Structure in Logics of Game Forms

• Davide Grossi
• Emiliano Lorini
• François Schwarzentruber

Structure of the paper. The article introduces a ceteris paribus modal logic interpreted on the equivalence classes induced by sets of propositional atoms. This logic is used to embed two logics of agency and games, namely atemporal STIT and the coalition logic of propositional control (CL−PC). The embeddings highlight a common ceteris paribus structure underpinning the key modal operators of both logics, they clarify the relationship between STIT and CL−PC, and enable the transfer of complexity results to the ceteris paribus logic. Section 2 introduces a logic called propositional equivalence ceteris paribus logic (PECP in short), which will be used as yardstick to analyze the game logics addressed in the paper. The logic will be axiomatized and briefly compared with existing modal logics of ceteris paribus reasoning. Section 3 provides a study of the relationship between the atemporal version of STIT and PECP. We show that PECP embeds atemporal group STIT—the fragment of atemporal STIT in which both actions of individuals and groups are represented—under the assumption that the agents’ choices are bounded. We call the latter atemporal ‘bounded’ group STIT. Moreover, we show that PECP embeds atemporal individual STIT—the variant of atemporal STIT in which only the actions of individuals are represented. The former embedding is used to transfer complexity results to PECP. We also present an embedding in PECP of a variant of atemporal group STIT in which groups are nested (i. e. , given two sets of agents J and J 0 either J ⊆ J 0 or viceversa). Section 4 provides an embedding of coalition logic of propositional control into atemporal ‘bounded’ group STIT and, indirectly, it provides an embedding of coalition logic of propositional control into PECP. We conclude in Section 5. Longer proofs are collected in a technical appendix at the end of the paper.

KR Conference 2012 Conference Paper

Fixpoints and Iterated Updates in Abstract Argumentation

• Davide Grossi

types of extensions (viz., grounded, complete, stable and preferred). Following the DEL methodology, these theorems are then analyzed in modal logic via iterated updates, making explicit their procedural nature and enabling precise epistemic interpretations of the approximation sequences. Technically, the paper exploits the link between abstract argumentation and modal logic investigated in (Grossi 2009; 2010) and applies notions on iterated updates developed in (Baltag and Smets 2009). Some of the results we present on approximation sequences of Dung’s extensions are inspired by old results on the logical analysis of self-reference (Yablo 1984). All in all, the paper lays a first bridge between DEL and argumentation theory. It is our hope that the results presented here could spark future interaction between these two lively fields of research which, although by different mathematical means, pursue strictly related questions. Fixpoints play a key role in the mathematical set up of abstract argumentation theory but, we argue, have been relatively underexamined in the literature. The paper studies the logical structure underlying the computation via approximation sequences of the sort of fixpoints relevant in argumentation. Concretely, it presents a number of novel results on the fixed point theory underpinning the main Dung’s semantics and, inspired by recent literature on the logical analysis of equilibrium computation in games, it provides a characterization of those semantics in terms of iterated model updates.

AAMAS Conference 2012 Conference Paper

Short Sight in Extensive Games

• Davide Grossi
• Paolo Turrini

The paper introduces a class of games in extensive form where players take strategic decisions while not having access to the terminal histories of the game, hence being unable to solve it by standard backwards induction. This class of games is studied along two directions: first, by providing an appropriate refinement of the subgame perfect equilibrium concept, a corresponding extension of the backwards induction algorithm and an equilibrium existence theorem; second, by showing that these games are a well-behaved subclass of a class of games with possibly unaware players recently studied in the literature.

LORI Conference 2011 Conference Paper

An Application of Model Checking Games to Abstract Argumentation

• Davide Grossi

Abstract The paper presents a logical study of abstract argumentation theory. It introduces a second-order modal logic, within which all main known semantics for abstract argumentation can be formalized, and studies the model checking game of this logic. The application of the game to the formalized semantics yields adequate game-theoretic proof procedures for all known extension-based semantics, in both their skeptical and credulous versions.

JAAMAS Journal 2011 Journal Article

Dependence in games and dependence games

• Davide Grossi
• Paolo Turrini

Abstract In the multi-agent systems community, dependence theory and game theory are often presented as two alternative perspectives on the analysis of agent interaction. The paper presents a formal analysis of a notion of dependence between players, given in terms of standard game-theoretic notions of rationality such as dominant strategy and best response. This brings the notion of dependence within the realm of game theory providing it with the sort of mathematical foundations which still lacks. Concretely, the paper presents two results: first, it shows how the proposed notion of dependence allows for an elegant characterization of a property of reciprocity for outcomes in strategic games; and second, it shows how the notion can be used to define new classes of coalitional games, where coalitions can force outcomes only in the presence of reciprocal dependencies.

AAMAS Conference 2010 Conference Paper

Dependence Theory via Game Theory

• Davide Grossi
• Paolo Turrini

In the multi-agent systems community, dependence theory and game theory are often presented as two alternative perspectives on the analysis of social interaction. Up till now no research has been done relating these two approaches. The unification presented provides dependence theory with the sort of mathematical foundations which still lacks, and shows how game theory can incorporate dependence-theoretic considerations in a fully formal manner.

AAMAS Conference 2010 Conference Paper

On the Logic of Argumentation Theory

• Davide Grossi

The paper applies modal logic to formalize fragments of argumentation theory. Such formalization allows to import, for free, a wealth of new notions (e. g. , argument equivalence), new techniques (e. g. , calculi, model-checking games, bisimulation games), and results (e. g. , completeness of calculi, adequacy of games, complexity of model-checking) fromlogic to argumentation.

LORI Conference 2009 Conference Paper

Dynamic Context Logic

• Guillaume Aucher
• Davide Grossi
• Andreas Herzig
• Emiliano Lorini

Abstract 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 show how it can capture some aspects of the dynamics of normative systems once they are viewed as logical theories.

LORI Conference 2009 Conference Paper

Twelve Angry Men: A Study on the Fine-Grain of Announcements

• Davide Grossi
• Fernando R. Velázquez-Quesada

Abstract By moving from a suggestive example, the paper analyzes how information flows among agents involved in a deliberation. By deliberating, agents become aware of details, draw the attention of the group to some issues, perform inferences and announce what they know. The proposed framework—which builds on the paradigm of dynamic logic—captures how, during a deliberation, information results from step-wise multi-agent interaction.

AAMAS Conference 2009 Conference Paper

Unifying Preference and Judgment Aggregation

• Davide Grossi

The paper proposes a unification of the two main frameworks commonly used for the analysis of collective decisionmaking: the framework of preference aggregation, developed from the seminal work of K. Arrow on social choice theory; and the more recent framework of judgment aggregation. Such unification provides several original insights on collective decision-making problems. The methods used are based on logic and, in particular, on formal semantics.

AAMAS Conference 2007 Conference Paper

A Formal Road from Institutional Norms to Organizational Structures

• Davide Grossi
• Frank Dignum
• John-Jules Ch. Meyer

Up to now, the way institutions and organizations have been used in the development of open systems has not often gone further than a useful heuristics. In order to develop systems actually implementing institutions and organizations, formal methods should take the place of heuristic ones. The paper presents a formal semantics for the notion of institution and its components (abstract and concrete norms, empowerment of agents, roles) and defines a formal relation between institutions and organizational structures. As a result, it is shown how institutional norms can be refined to constructs–organizational structures–which are closer to an implemented system. It is also shown how such a refinement process can be fully formalized and it is therefore amenable to rigorous verification.

AILAW Journal 2007 Journal Article

From human regulations to regulated software agents’ behavior

• Javier Vázquez-Salceda
• Huib Aldewereld
• Davide Grossi
• Frank Dignum

Abstract In order to design and implement electronic institutions that incorporate norms governing the behavior of the participants of those institutions, some crucial steps should be taken. The first problem is that human norms are (on purpose) specified on an abstract level. This ensures applicability of the norms over long periods of time in many different circumstances. However, for an electronic institution to function according to those norms, they should be concrete enough to be able to check them run time. A second problem is that norms describe which behavior is desirable and permitted, but not how this is achieved in an institution. In the “real world" regulations often indicate procedures for implementing and enforcing the law. Likewise we should devise means to annotate the norms with practical aspects such as enforcement mechanisms, sanctions, etc. in order to get requirements for an institution that will enforce norms (by either constraining behavior within the norms or reacting to violation of the norms). The choice of which kind of mechanism is chosen is not a normative one, but usually based on criteria of efficiency and/or feasibility of the mechanism. In this paper we present our view on how to approach these problems and other related issues to be solved in order to develop e-institutions capable to operate in complex, highly regulated scenarios.

AILAW Journal 2007 Journal Article

Organizational structure and responsibility

• Davide Grossi
• Lambèr Royakkers
• Frank Dignum

Abstract Aim of the present paper is to provide a formal characterization of various different notions of responsibility within groups of agents (Who did that? Who gets the blame? Who is accountable for that? etc.). To pursue this aim, the papers proposes an organic analysis of organized collective agency by tackling the issues of organizational structure, role enactment, organizational activities, task-division and task-allocation. The result consists in a semantic framework based on dynamic logic in which all these concepts can be represented and in which various notions of responsibility find a formalization. The background motivation of the work consists in those responsibility-related issues which are of particular interest for the theory and development of multi-agent systems.

AAMAS Conference 2006 Conference Paper

Structural Evaluation of Agent Organizations

• Davide Grossi
• Frank Dignum
• Virginia Dignum
• Mehdi Dastani
• Lamber Royakkers

AAMAS Conference 2005 Conference Paper

Foundations of Organizational Structures in Multi-Agent Systems

• Davide Grossi
• Frank Dignum
• Lamber Royakkers
• Mehdi Dastani