Tight Logic Programs

This note is about the relationship between two theories of negation as failure -- one based on program completion, the other based on stable models, or answer sets. Francois Fages showed that if a logic program satisfies a certain syntactic condition, which is now called ``tightness,'' then its stable models can be characterized as the models of its completion. We extend the definition of tightness and Fages' theorem to programs with nested expressions in the bodies of rules, and study tight logic programs containing the definition of the transitive closure of a predicate.Comment: To appear in Special Issue of the Theory and Practice of Logic Programming Journal on Answer Set Programming, 200

Migraciones desde el "Sur Global" y la economía informal en Turquía, ¿Laissez passer, laissez faire?

En términos de movimientos migratorios desde el “Sur Global”, Turquía es a un tiempo país receptor, de tránsito y emisor. Este trabajo analiza estos flujos auto-organizados a través del concepto de la “autonomía de la migración”. El trabajo comienza por delinear el impacto de la ideología nacionalista turca en los movimientos migratorios. A continuación, se estudia la economía de las migraciones de tránsito que sostiene los flujos contemporáneos, dados los controles en frontera, más estrictos que nunca, impuestos como parte del proceso de acceso de Turquía a la UE. Seguidamente, se estudia la emigración laboral a países europeos y de Oriente Medio. Finalmente, se examina el acceso diferencial de los migrantes al empleo informal en Turquía, a la luz de resultados de investigación recientes. Se identifican el género, la etnicidad y las redes sociales como factores que enmarcan las migraciones. _______________________________________In terms of migratory movements from the “Global South”, Turkey is a receiving, transit and sending country all at the same time. The paper analyzes these self-organized flows through the concept of the “autonomy of migration”. The paper starts off by outlining the defining impact of Turkish nationalist ideology on migratory movements. Next, the economy of transit migration that sustains contemporary flows is analyzed, given ever stricter border controls implemented as part of the Turkey’s process of EU acquis. Next labour emigration to European and the Middle Eastern countries is reviewed. Lastly, the differential access of migrants to informal employment in Turkey is examined in light of recent research findings. Gender, ethnicity and social networks are identified as factors that frame migrant agency

Temporal Phylogenetic Networks and Logic Programming

The concept of a temporal phylogenetic network is a mathematical model of evolution of a family of natural languages. It takes into account the fact that languages can trade their characteristics with each other when linguistic communities are in contact, and also that a contact is only possible when the languages are spoken at the same time. We show how computational methods of answer set programming and constraint logic programming can be used to generate plausible conjectures about contacts between prehistoric linguistic communities, and illustrate our approach by applying it to the evolutionary history of Indo-European languages. To appear in Theory and Practice of Logic Programming (TPLP)

Fages' Theorem and Answer Set Programming

We generalize a theorem by Francois Fages that describes the relationship between the completion semantics and the answer set semantics for logic programs with negation as failure. The study of this relationship is important in connection with the emergence of answer set programming. Whenever the two semantics are equivalent, answer sets can be computed by a satisfiability solver, and the use of answer set solvers such as smodels and dlv is unnecessary. A logic programming representation of the blocks world due to Ilkka Niemelae is discussed as an example

Explanation Generation for Multi-Modal Multi-Agent Path Finding with Optimal Resource Utilization using Answer Set Programming

The multi-agent path finding (MAPF) problem is a combinatorial search problem that aims at finding paths for multiple agents (e.g., robots) in an environment (e.g., an autonomous warehouse) such that no two agents collide with each other, and subject to some constraints on the lengths of paths. We consider a general version of MAPF, called mMAPF, that involves multi-modal transportation modes (e.g., due to velocity constraints) and consumption of different types of resources (e.g., batteries). The real-world applications of mMAPF require flexibility (e.g., solving variations of mMAPF) as well as explainability. Our earlier studies on mMAPF have focused on the former challenge of flexibility. In this study, we focus on the latter challenge of explainability, and introduce a method for generating explanations for queries regarding the feasibility and optimality of solutions, the nonexistence of solutions, and the observations about solutions. Our method is based on answer set programming. This paper is under consideration for acceptance in TPLP.Comment: Paper presented at the 36th International Conference on Logic Programming (ICLP 2020), University Of Calabria, Rende (CS), Italy, September 2020, 16 pages, 6 figure