Lluis Godo

FLAP Journal 2025 Journal Article

Defeasible Argumentation-based Epistemic Planning with Preferences

• Juan C. L. Teze
• Lluis Godo
• Gerardo I. Simari

Many real-world applications of intelligent systems involve solving planning problems of different nature, oftentimes in dynamic environments and having to deal with potentially contradictory information, leading to what is com- monly known as epistemic planning. In this context, defeasible argumentation is a powerful tool that has been developed for over three decades as a practi- cal mechanism that allows for flexible handling of preferences and explainable reasoning. In this article, we first motivate the need to develop argumentation- based epistemic planning frameworks that can be leveraged in real-world ap- plications, describe the related literature, and then provide an overview of a recently-proposed approach to incorporate defeasible argumentation and pref- erences into automated planning processes. In particular, the framework in- corporates conditional expressions to select and change priorities regarding in- formation upon which plans are constructed. We describe its main properties, analyze its strengths and limitations using an illustrative use case, and discuss several future research directions that can be taken to further develop it.

KR Conference 2024 Conference Paper

Possibility of Conditionals and Conditional Possibilities: From the Triviality Result to Possibilistic Imaging

• Tommaso Flaminio
• Lluis Godo
• Giuliano Rosella

Lewis-Gärdenfors imaging is an updating procedure for probability functions that generalizes Bayesian conditionalization, allowing to approach the probability of conditionals and counterfactual formulas without incurring in Lewis well-known triviality result. Precisely, while the probability of a so called Stalnaker conditional (as formalizable in Lewis logic C2) was proved to be an imaged probability by Lewis in his celebrated paper from 1976, a variant of Gärdenfors generalized imaging (proposed by Dubois and Prade in 1994) has been recently proved to characterize the probability of Lewis counterfactuals, the latter refer to those conditionals of Lewis’s logic C1. The present contribution extends the analysis on Lewis’s triviality result, imaging and generalized imaging to cope with possibility and necessity measures. In particular, after showing that the triviality result also holds in the possibilistic framework, we introduce a way to define the possibility measure of conditional and counterfactual formula. Then we prove that the possibilistic version of Lewis-Gärdenfors imaging (that is inspired by a definition given again by Dubois and Prade in 1994) actually characterizes, as in the aforementioned cases, the possibility of Stalnaker conditionals and Lewis counterfactuals. Furthermore, we show that possibilistic imaging can also be described within the setting of Boolean algebras of conditionals and Lewis algebras. These are algebraic models for conditional and counterfactual formulas recently introduced by two of the present authors. On these structures one can (canonically) define a notion of possibility measure that turns out to be the conditional possibility and imaged possibility mentioned above, respectively, and hence it represents the possibility of conditional and counterfactual formulas.

KR Conference 2022 Conference Paper

Compound Conditionals as Random Quantities and Boolean Algebras

• Tommaso Flaminio
• Angelo Gilio
• Lluis Godo
• Giuseppe Sanfilippo

Conditionals play a key role in different areas of logic and probabilistic reasoning, and they have been studied and formalised from different angles. In this paper we focus on the de Finetti's notion of conditional as a three-valued object, with betting-based semantics, and its related approach as random quantity as mainly developed by two of the authors. Compound conditionals have been studied in the literature, but not in full generality. In this paper we provide a natural procedure to explicitly attach conditional random quantities to arbitrary compound conditionals that also allows us to compute their previsions. By studying the properties of these random quantities, we show that, in fact, the set of compound conditionals can be endowed with a Boolean algebraic structure. In doing so, we pave the way to build a bridge between the long standing tradition of three-valued conditionals and a more recent proposal of looking at conditionals as elements from suitable Boolean algebras.

IS Journal 2021 Journal Article

An Architecture for Argumentation-Based Epistemic Planning: A First Approach With Contextual Preferences

• Juan Carlos Teze
• Lluis Godo

Argumentation-based planning systems present an interesting proposal for complex and dynamic domains where defeasible argumentation is used in the reasoning processes during the construction of plans by considering the available knowledge. In many real-world application scenarios, knowledge is provided with explicit priorities. Despite its importance, existing planning systems do not provide additional reasoning capacities of dynamically changing the preferences expressed by these priorities when a plan is being constructed. In this article, we present an argumentation and planning architecture, and propose a set of software engineering guidelines to analyze and design planning systems leveraging this capacity.

AIJ Journal 2020 Journal Article

Boolean algebras of conditionals, probability and logic

• Tommaso Flaminio
• Lluis Godo
• Hykel Hosni

This paper presents an investigation on the structure of conditional events and on the probability measures which arise naturally in that context. In particular we introduce a construction which defines a (finite) Boolean algebra of conditionals from any (finite) Boolean algebra of events. By doing so we distinguish the properties of conditional events which depend on probability and those which are intrinsic to the logico-algebraic structure of conditionals. Our main result provides a way to regard standard two-place conditional probabilities as one-place probability functions on conditional events. We also consider a logical counterpart of our Boolean algebras of conditionals with links to preferential consequence relations for non-monotonic reasoning. The overall framework of this paper provides a novel perspective on the rich interplay between logic and probability in the representation of conditional knowledge.

AAMAS Conference 2006 Conference Paper

Negotiating using Rewards

• Sarvapali Ramchurn
• Carles Sierra
• Lluis Godo
• NICK JENNINGS

IJCAI Conference 1995 Conference Paper

Possibihstic Temporal Reasoning based on Fuzzy Temporal Constraints

• Lluis Godo
• Lluls Vila

In this paper we propose a propositional temporal language based on fuzzy temporal constraints which turns out to be expressive enough for domains -like many coming from medicine- where knowledge is of propositional nature and an explicit handling of time, imprecision and uncertainty are required. The language is provided with a natural possibilistic semantics to account for the uncertainty issued by the fuzziness of temporal constraints. We also present an inference system based on specific rules dealing with the temporal constraints and a general fuzzy modus ponens rule whereby behaviour is shown to be sound. The analysis of the different choices as fuzzy operators leads us to identify the well-known Lukasiewicz implication as very appropriate to define the notion of possibilistic entailment, an essential element of our inference system.