New Zealand


We present two logics of collective belief with a semantics exploiting the notion of belief base. The semantics distinguishes explicit from implicit belief: an agent&#39;s belief of explicit type is a piece of information contained in the agent&#39;s belief base, while a belief of implicit type corresponds to a piece of information that is derivable from the agent&#39;s belief base. The first part of the paper is devoted to the logic of implicit common belief, while the second presents the logic of explicit common belief. Implicit common belief is defined as a mutual belief of any order. This leads to the usual fixpoint construction of common belief. Explicit common belief is the collective counterpart of explicit individual belief and has a public nature. It moreover implies implicit common belief. We study axiomatic aspects of our logics as well as complexity of satisfiability checking. We show that, while the satisfiability checking problem is EXPTIME-hard for the logic of implicit common belief, it is in PSPACE for the logic of explicit common belief. This makes the latter logic a natural candidate for reasoning about collective attitudes of agents in multi-agent scenarios and applications. We also study a dynamic extension of the logic of explicit common belief in which private and public forms of information dynamics can be modeled.

AAMAS 2022

Logical Theories of Collective Attitudes and the Belief Base Perspective

reasoning about beliefs

collective attitudes

modal logic

epistemic logic

AAMAS (International Conference on Autonomous Agents and Multiagent Systems) is the largest and most influential conference in the area of agents and multiagent systems. The aim of the conference is to bring together researchers and practitioners in all areas of agent technology and to provide a single, high-profile, internationally renowned forum for research in the theory and practice of autonomous agents and multiagent systems. AAMAS is the flagship conference of the non-profit International Foundation for Autonomous Agents and Multiagent Systems (IFAAMAS).

The AAMAS conference series was initiated in 2002 in Bologna, Italy as a joint event comprising the 6th International Conference on Autonomous Agents (AA), the 5th International Conference on Multiagent Systems (ICMAS), and the 9th International Workshop on Agent Theories, Architectures, and Languages (ATAL).

Subsequent AAMAS conferences have been held in Melbourne, Australia (July 2003), New York City, NY, USA (July 2004), Utrecht, The Netherlands (July 2005), Hakodate, Japan (May 2006), Honolulu, Hawaii, USA (May 2007), Estoril, Portugal (May 2008), Budapest, Hungary (May 2009), Toronto, Canada (May 2010), Taipei, Taiwan (May 2011), Valencia, Spain (June 2012), Minnesota, USA (May 2013), Paris, France (May 2014), Istanbul, Turkey (May 2015), Singapore (May 2016), São Paulo (2017) and Stockholm, Sweden (2018), Montreal (May 2019), Auckland (May 2020, Virtual), London (May 2021, Virtual).
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AAMAS (International Conference on Autonomous Agents and Multiagent Systems) is the largest and most influential conference in the area of agents and multiagent systems. The aim of the conference is to bring together researchers and practitioners in all areas of agent technology and to provide a single, high-profile, internationally renowned forum for research in the theory and practice of autonomous agents and multiagent systems. AAMAS is the flagship conference of the non-profit International Foundation for Autonomous Agents and Multiagent Systems (IFAAMAS).


We present two logics of collective belief with a semantics exploiting the notion of belief base. The semantics distinguishes explicit from implicit belief: an agent's belief of explicit type is a piece of information contained in the agent's belief base, while a belief of implicit type corresponds to a piece of information that is derivable from the agent's belief base. The first part of the paper is devoted to the logic of implicit common belief, while the second presents the logic of explicit common belief. Implicit common belief is defined as a mutual belief of any order. This leads to the usual fixpoint construction of common belief. Explicit common belief is the collective counterpart of explicit individual belief and has a public nature. It moreover implies implicit common belief. We study axiomatic aspects of our logics as well as complexity of satisfiability checking. We show that, while the satisfiability checking problem is EXPTIME-hard for the logic of implicit common belief, it is in PSPACE for the logic of explicit common belief. This makes the latter logic a natural candidate for reasoning about collective attitudes of agents in multi-agent scenarios and applications. We also study a dynamic extension of the logic of explicit common belief in which private and public forms of information dynamics can be modeled.

technical paper


Computational agents based on the BDI framework typically rely on abstract plans and plan refinement to reach a degree of autonomy in dynamic environments: agents are provided with the ability to select how-to achieve their goals by choosing from a set of options. In this work we focus on a related, yet under-studied feature: abstract goals. These constructs refer to the ability of agents to adopt goals that are not fully grounded at the moment of invocation, refining them only when and where needed: the ability to select what-to (concretely) achieve at run-time. We present a reference-based approach to goal refinement, defining preferences based on extended Ceteris Paribus Networks (CP-Nets) for an AgentSpeak(L)-like agent programming language, and utilizing the established CP-Nets logic and algorithms to guide the goal refinement step. As a technical contribution, we present an implementation of this method that solely uses a Prolog-like inference engine of the agent's belief-base to reason about preferences, thus minimally affecting the decision-making mechanisms hard-coded in the agent framework.

Preference-Based Goal Refinement in BDI Agents


The original BOID is a cognitive architecture that unifies Belief, Obligation, Intention and Desire rules to calculate which actions should an agent undertake next. In the current paper, we adapt the original BOID with an aim to model autonomous agency. The new BOID* architecture is able to capture anticipation that we believe to be one of the hallmarks of autonomous agency. We focus on developing algorithms for anticipatory reasoning through a new BOID* goal deliberation component. The key method that BOID* introduces is abductive reasoning as a way to represent motivational attitudes, such as desires and obligations. As a result of deliberation via abduction, BOID* specifies intention revision procedures that connect motivational and informational attitudes. The BOID* is a part of the project to build autonomous AI models that make explicit the reasoning behind adopting future goals, prioritizing selected goals and forming intentions.

BOID*: Autonomous goal deliberation through abduction


This paper presents a new multi-agent model for simulating malware
propagation in device-to-device (D2D) 5G networks. This model
allows to understand and analyze mobile malware spreading dynamics in such highly dynamical networks. Additionally, we present a
theoretical study to validate and benchmark our proposed approach
for some basic scenarios that are less complicated to model mathematically and also to highlight the key parameters of the model. Our
simulations identifying critical thresholds for "no propagation" and
for "maximum malware propagation" and make predictions on the
malware spread velocity as well as device infection rates. To the best
of our knowledge, this paper is the first study applying agent-based
simulations for malware propagation in D2D.

Agent-based modeling and simulation for malware spreading in D2D networks


Agents have been used for simulating cultural evolution and cultural evolution can be used as a model for artificial agents. Previous results have shown that horizontal, or intra-generation, knowledge transmission allows agents to improve the quality of their knowledge to a certain level. Moreover, variation generated through vertical, or inter-generation, transmission allows agents to exceed that level. Such results have been obtained under specific conditions such as the drastic selection of agents allowed to transmit their knowledge, seeding the process with correct knowledge or introducing artificial noise during transmission. Here, we question the necessity of such measures and study their impact on the quality of transmitted knowledge. For that purpose, we combine the settings of two previous experiments and we relax these assumptions (no strong selection of teachers, no fully correct seed, no introduction of artificial noise). The rationale is that if interactions lead agents to improve their overall knowledge quality, this should be sufficient to ensure correct knowledge transmission, and that transmission mechanisms are sufficiently imperfect to produce variation. In this setting, we confirm that vertical transmission improves on horizontal transmission even without drastic selection and oriented learning. We also show that horizontal transmission is able to compensate for the lack of parent selection if it is maintained for long enough. This shows that it is not necessary to take the most successful agents as teachers, neither in vertical nor horizontal transmission, to cumulatively improve knowledge.

Knowledge Transmission and Improvement Across Generations do not Need Strong Selection


Ants have evolved to seek and retrieve food by leaving trails of pheromones. This mechanism has inspired several approaches to decentralized multi-robot coordination. However, in this paper, we show that pheromone trails are a fragile mechanism for coordination, and can be sabotaged to starve the colony. We introduce detractors: malicious agents that leave a misleading, but indistinguishable, trail of food pheromone to distract and trap cooperator ants in the nest. We analyze the effectiveness of detractors with respect to parameters such as evaporation rate of misleading pheromone and fraction of detractors in the colony. In addition, we propose a countermeasure to this attack by introducing a new type of pheromone: the cautionary pheromone. Cooperator ants secrete this type of pheromone atop existing food trails as a warning. When the cautionary pheromone intensity exceeds the food pheromone intensity, cooperator ants ignore overlapping food pheromone. We show that, despite its simplicity, this defense mechanism can limit, but not nullify, the effect of detractors. Ultimately, our work shows that pheromone-based coordination, while effective, is also fragile.

Hacking the Colony: On the Disruptive Effect of Misleading Pheromone and How to Defend against It


The trustors in a reputation system share trust-relevant information amongst themselves about trustees. 
If there is lag present in the sharing mechanism, a malicious trustee can exploit it to perform additional bad actions that would not be permitted otherwise. 
This is the reputation lag attack. 
In this paper, we use a simulation model to explore properties of the reputation lag attack, attack strategies which improve the attacker's success and factors which mitigate the attacker. 
In particular, we demonstrate the following key findings: 
Attackers in lagged systems clearly outperform attackers in lag-free systems.
The attacker's success is proportional to their rate of action until a plateau at the maximum number of bad actions. 
Attackers which wait for their good reputation to disseminate outperform those who do not. 
Attackers which perform only good actions, wait for dissemination and then perform only bad actions outperform attackers who do not follow such an ordering.
Using centrality metrics to target users improves the attacker's performance.
Temporarily avoiding users that reject them will improve the attacker's performance.
Putting a time-decay on the information value of a message will worsen an ordered attacker.
A network with a homogeneous structure will worsen the performance of a centrality-targetting attacker.
To summarize, we demonstrate not only the viability of the reputation lag attack in our model but also the presence of strategies that both aid and mitigate the attacker.

Properties of Reputation Lag Attack Strategies


A classical problem in the fair allocation literature is finding an envy-free assignment of indivisible resources to agents with additive utility-based preferences over resources. Motivated by the possible non-existence but evident need of envy-free allocations in some applications, we study the following problem modeling one possible way out: Given an allocation of indivisible resources to agents, is it possible to socially donate some of the resources (which means removing these resources from the allocation instance) such that the resulting modified allocation is envy-free (up to one good). We require that the number of deleted resources and/or the caused utilitarian welfare loss of the allocation are bounded. We conduct a thorough study of the (parameterized) computational complexity of this problem considering various natural and problem-specific parameters (e.g., the number of agents, the number of deleted resources, or the maximum number of resources assigned to an agent in the initial allocation) and different preference models, including unary and 0/1-valuations. In our studies, we obtain a rich set of (parameterized) tractability and intractability results and discover several surprising contrasts, for instance, between the two closely related fairness concepts envy-freeness and envy-freeness up to one good and between the influence of the parameters maximum number and welfare of the deleted resources.

Multivariate Algorithmics for Eliminating Envy by Donating Goods


The notion of envy-freeness is a natural and intuitive fairness requirement in resource allocation. With indivisible goods, such fair allocations are unfortunately not guaranteed to exist. Classical works have avoided this issue by introducing an additional divisible resource, i.e., money, to subsidize envious agents. In this paper, we aim to design a truthful allocation mechanism of indivisible goods to achieve both fairness and efficiency criteria with a limited amount of subsidy. Following the work of Halpern and Shah, our central question is as follows: to what extent do we need to rely on the power of money to accomplish these objectives? We show that, when agents have matroidal valuations, there is a truthful allocation mechanism that achieves envy-freeness and utilitarian optimality by subsidizing each agent with at most 1, the maximum marginal contribution of each item for each agent. The design of the mechanism rests crucially on the underlying matroidal M-convexity of the Lorenz dominating allocations. For superadditive valuations, we show that there is a truthful mechanism that achieves envy-freeness and utilitarian optimality, with each agent receiving a subsidy of at most m; furthermore, we show that the amount m is necessary even when agents have additive valuations.

Fair and Truthful Mechanism with Limited Subsidy


We study the problem of fairly allocating a set of $m$ indivisible chores (i.e. items with non-positive value) to $n$ agents. We consider the desirable fairness notion of $1$-out-of-$d$ maximin share (MMS)---the minimum value that an agent can guarantee by partitioning items into $d$ bundles and selecting the least valued bundle---and focus on ordinal approximation of MMS that aims at finding the largest $d$ for which $1$-out-of-$d$ MMS exists. Our main theoretical contribution is showing the existence of $1$-out-of-$\lfloor\frac{3n}{4}\rfloor$ MMS allocations and proving that $1$-out-of-$\lfloor\frac{2n}{3}\rfloor$ MMS allocations of chores can be computed in polynomial time. Furthermore, we show that practical polynomial-time algorithms exist for approximating $1$-out-of-$\lfloor\frac{3n}{4}\rfloor$ MMS bound for chores. This is in contrast to computing allocations that guarantee a fraction of MMS to each agent, where only a polynomial-time approximation scheme (PTAS) with run-time exponential in the approximation accuracy $1/\epsilon$ is known.

Ordinal Maximin Share Approximation for Chores


The problem of fair division known as ``cake cutting'' has been the focus of multiple papers spanning several decades. The most prominent problem in this line of work has been to bound the query complexity of computing an envy-free outcome in the Robertson-Webb query model. However, the root of this problem's complexity is somewhat artificial: the agents' values are assumed to be additive across different pieces of the ``cake'' but infinitely complicated within each piece. This is unrealistic in most of the motivating examples, where the cake represents a finite collection of homogeneous goods. 

We address this issue by introducing a fair division model that more accurately captures these applications: the value that an agent gains from a given good depends only on the amount of the good they receive, yet it can be an arbitrary function of this amount, allowing the agents to express preferences that go beyond standard cake cutting. In this model, we study the query complexity of computing allocations that are not just envy-free, but also approximately Pareto optimal among all envy-free allocations. Using a novel flow-based approach, we show that we can encode the ex-post feasibility of randomized allocations via a polynomial number of constraints, which reduces our problem to solving a linear program.

Logical Theories of Collective Attitudes and the Belief Base Perspective

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