University of Corunna

of Corunna, Spain

University of Corunna

of Corunna, Spain

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Cabalar P.,University of Corunna
AI Communications | Year: 2011

In this paper we consider a logical treatment for the ordered disjunction operator × introduced by Brewka, Niemelä and Syrjänen in their Logic Programs with Ordered Disjunctions (LPOD). LPODs are used to represent preferences in logic programming under the answer set semantics. Their semantics is defined by first translating the LPOD into a set of normal programs (called split programs) and then imposing a preference relation among the answer sets of these split programs. We concentrate on the first step and show how a suitable translation of the ordered disjunction as a derived operator into the logic of Here-and-There allows capturing the answer sets of the split programs in a direct way. We use this characterisation not only for providing an alternative implementation for LPODs, but also for checking several properties (under strongly equivalent transformations) of the × operator, like for instance, its distributivity with respect to conjunction or regular disjunction. We also make a comparison to an extension proposed by Kärger, Lopes, Olmedilla and Polleres, that combines × with regular disjunction. © 2011 IOS Press and the authors. All rights reserved.


Cabalar P.,University of Corunna | Santos P.E.,State University of Maringa
Artificial Intelligence | Year: 2016

This research note contains an extension of a previous work by Cabalar and Santos (2011) that formalised several spatial puzzles formed by strings and holes. That approach explicitly ignored some configurations and actions that were irrelevant for the studied puzzles but are physically possible and may become crucial for other spatial reasoning problems. In particular, the previous work did not consider the formation of string loops or the situations where a holed object is partially crossed by another holed object. In this paper, we remove these limitations by treating string loops as dynamic holes that can be created or destroyed by a pair of elementary actions, respectively picking or pulling from strings. We explain how string loops can be recognised in a data structure representing the domain states and define a notation to represent crossings through string loops. The resulting formalism is dual in the sense that it also allows understanding any hole as a kind of (sometimes rigid) closed string loop. © 2016 Published by Elsevier B.V.


Fandinno J.,University of Corunna
Theory and Practice of Logic Programming | Year: 2016

We present an extension of Logic Programming (under stable models semantics) that, not only allows concluding whether a true atom is a cause of another atom, but also deriving new conclusions from these causal-effect relations. This is expressive enough to capture informal rules like if some agent's actions have been necessary to cause an event E then conclude atom caused(, E), something that, to the best of our knowledge, had not been formalised in the literature. To this aim, we start from a first attempt that proposed extending the syntax of logic programs with so-called causal literals. These causal literals are expressions that can be used in rule bodies and allow inspecting the derivation of some atom A in the program with respect to some query function ψ. Depending on how these query functions are defined, we can model different types of causal relations such as sufficient, necessary or contributory causes, for instance. The initial approach was specifically focused on monotonic query functions. This was enough to cover sufficient cause-effect relations but, unfortunately, necessary and contributory are essentially non-monotonic. In this work, we define a semantics for non-monotonic causal literals showing that, not only extends the stable model semantics for normal logic programs, but also preserves many of its usual desirable properties for the extended syntax. Using this new semantics, we provide precise definitions of necessary and contributory causal relations and briefly explain their behaviour on a pair of typical examples from the Knowledge Representation literature. © 2016 Cambridge University Press.


Cabalar P.,University of Corunna | Fandinno J.,University of Corunna
Theory and Practice of Logic Programming | Year: 2016

In this paper, we study an extension of the stable model semantics for disjunctive logic programs where each true atom in a model is associated with an algebraic expression (in terms of rule labels) that represents its justifications. As in our previous work for non-disjunctive programs, these justifications are obtained in a purely semantic way, by algebraic operations (product, addition and application) on a lattice of causal values. Our new definition extends the concept of causal stable model to disjunctive logic programs and satisfies that each (standard) stable model corresponds to a disjoint class of causal stable models sharing the same truth assignments, but possibly varying the obtained explanations. We provide a pair of illustrative examples showing the behaviour of the new semantics and discuss the need of introducing a new type of rule, which we call causal-choice. This type of rule intuitively captures the idea of A may cause B and, when causal information is disregarded, amounts to a usual choice rule under the standard stable model semantics. © 2016 Cambridge University Press.


Cabalar P.,University of Corunna | Dieguez M.,University of Corunna
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2011

In this paper we present STeLP, a solver for Answer Set Programming with temporal operators. Taking as an input a particular kind of logic program with modal operators (called Splitable Temporal Logic Program), STeLP obtains its set of temporal equilibrium models (a generalisation of stable models for this extended syntax). The obtained set of models is represented in terms of a deterministic Büchi automaton capturing the complete program behaviour. In small examples, this automaton can be graphically displayed in a direct and readable way. The input language provides a set of constructs which allow a simple definition of temporal logic programs, including a special syntax for action domains that can be exploited to simplify the graphical output. STeLP combines the use of a standard ASP solver with a linear temporal logic model checker in order to find all models of the input theory. © 2011 Springer-Verlag Berlin Heidelberg.


Dieguez M.,University of Corunna
Leibniz International Proceedings in Informatics, LIPIcs | Year: 2012

Answer Set Programming (ASP) has become a popular way for representing different kinds of scenarios from knowledge representation in Artificial Intelligence. Frequently, these scenarios involve a temporal component which must be considered. In ASP, time is usually represented as a variable whose values are defined by an extensional predicate with a finite domain. Dealing with a finite temporal interval has some disadvantages. First, checking the existence of a plan is not possible and second, it also makes difficult to decide whether two programs are strongly equivalent. If we extend the syntax of Answer Set Programming by using temporal operators from temporal modal logics, then infinite time can be considered, so the aforementioned disadvantages can be overcome. This extension constitutes, in fact, a formalism called Temporal Equilibrium Logic, which is based on Equilibrium Logic (a logical characterisation of ASP). Although recent contributions have shown promising results, Temporal Equilibrium Logic is still a novel paradigm and there are many gaps to fill. Our goal is to keep developing this paradigm, filling those gaps and turning it into a suitable framework for temporal reasoning. © Martín Diéguez.


Cabalar P.,University of Corunna | Santos P.E.,State University of Maringa
Artificial Intelligence | Year: 2010

This paper investigates the challenging problem of encoding the common sense knowledge involved in the manipulation of spatial objects from a reasoning about actions and change perspective. In particular, we propose a formal solution to a puzzle composed of non-trivial objects (such as holes and strings) assuming a version of the Situation Calculus written over first-order Equilibrium Logic, whose models generalise the stable model semantics. © 2010 Elsevier B.V. All rights reserved.


Cabalar P.,University of Corunna
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2010

In previous work, the so-called Temporal Equilibrium Logic (TEL) was introduced. This formalism provides an extension of the Answer Set semantics for logic programs to arbitrary theories in the syntax of Linear Temporal Logic. It has already been shown that, in the non-temporal case, arbitrary propositional theories can always be reduced to logic program rules (with disjunction and negation in the head) independently on the context. That is, logic programs constitute a normal form for the non-temporal case. In this paper we show that TEL can be similarly reduced to a normal form consisting of a set of implications (embraced by a necessity operator) quite close to logic program rules. This normal form may be useful both for a practical implementation of TEL and a simpler analysis of theoretical problems. © 2010 Springer-Verlag.


Cabalar P.,University of Corunna
Theory and Practice of Logic Programming | Year: 2011

In this paper we propose an extension of Answer Set Programming (ASP) to deal with (possibly partial) evaluable functions. To this aim, we start from the most general logical counterpart of ASP, Quantified Equilibrium Logic (QEL), and propose a variant QEL= f where the set of functions is partitioned into Herbrand functions (or constructors) and evaluable functions (or operations). We show how this extension has a direct connection to Scott's Logic of Existence, and introduce several useful derived operators, some of them directly borrowed from Scott's formalisation. Using this general framework for arbitrary theories, we proceed to focus on a syntactic subclass that corresponds to normal logic programs with evaluable functions and equality. We provide a translation of this class into function-free normal programs and consider a safety condition so that the resulting program is also safe, under the usual meaning in ASP. Finally, we also establish a formal comparison to Lin and Wang's approach (FASP) dealing with evaluable total functions. © 2011 Cambridge University Press.


Garcia-Garcia O.,University of Vigo | Cancela-Carral J.M.,University of Vigo | Martinez-Trigo R.,University of Vigo | Serrano-Gomez V.,University of Corunna
Journal of Strength and Conditioning Research | Year: 2013

The purpose of this study was to establish reference values of tensiomyography (TMG) in professional road cyclists and to examine how the planned periods of the Season produce differences in the muscles: vastus medialis (VM), vastus lateralis (VL), rectus femoris (RF), and biceps femoris (BF), and to determine how these differences may depend on each cyclist, the assessed muscle, and the side of the body. Ten professional road cyclists (27.5 6 5.5 years; 178.2 6 7.8 cm; 65.6 6 5.46 kg; 72.1 6 3.7 mlkg21min21 V O2; 6 6 0.4 Wkg21) were assessed by TMG, in microcycle recovery, at 2 moments of periods during the season: preparation period (PP) and competition period (CP). Student's t contrast for paired groups, Cohen's d effect sizes, and a repeated measures analysis of variance (ANOVA) was applied. We did not find significant differences (p , 0.01) between the lower limbs. The results showed a significantly large increment between the time contraction (TC) values of the PP and CP in the muscles VM (28.7 6 5.5 vs. 40.6 6 14.4 milliseconds; 41.4%, p , 0.05, d = 1.1), VL (28.3 6 4.9 vs. 40.6 6 10.2 milliseconds; 43.4%, p , 0.05, d = 1.53), and RF (35.9 6 6.9 vs. 45.9 6 16.2 milliseconds; 27.8%, p , 0.05, d = 0.8). Nevertheless, TC of the BF presents a significantly large decrease in the CP (35.9 6 9.9 vs. 28.2 6 5.2 milliseconds; 221.4%, p , 0.05, d = 0.97). Radial muscle displacement (DM) values are slightly lower during the CP, but the difference is not significant. ANOVA confirmed that these differences depend on the evaluated muscles (TC p = 0.02; DM p = 0.001) and on the cyclists (TC p = 0.001; DM p = 0.001) and does not depend on the side of the body. In conclusion, the TC values during the Season show marked differences between the knee extensors (large increased) and the knee flexor (large decreased). The DM has not changed significantly, keeping the muscular and tendon stiffness. © 2013 National Strength and Conditioning Association.

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