TY  - JOUR
A1  - Cabalar, Pedro
A1  - Fandinno, Jorge
A1  - Garea, Javier
A1  - Romero, Javier
A1  - Schaub, Torsten H.
T1  - Eclingo
BT  - a solver for epistemic logic programs
JF  - Theory and practice of logic programming
N2  - We describe eclingo, a solver for epistemic logic programs under Gelfond 1991 semantics built upon the Answer Set Programming system clingo. The input language of eclingo uses the syntax extension capabilities of clingo to define subjective literals that, as usual in epistemic logic programs, allow for checking the truth of a regular literal in all or in some of the answer sets of a program. The eclingo solving process follows a guess and check strategy. It first generates potential truth values for subjective literals and, in a second step, it checks the obtained result with respect to the cautious and brave consequences of the program. This process is implemented using the multi-shot functionalities of clingo. We have also implemented some optimisations, aiming at reducing the search space and, therefore, increasing eclingo 's efficiency in some scenarios. Finally, we compare the efficiency of eclingo with two state-of-the-art solvers for epistemic logic programs on a pair of benchmark scenarios and show that eclingo generally outperforms their obtained results.
KW  - Answer Set Programming
KW  - Epistemic Logic Programs
KW  - Non-Monotonic
KW  - Reasoning
KW  - Conformant Planning
Y1  - 2020
U6  - https://doi.org/10.1017/S1471068420000228
SN  - 1471-0684
SN  - 1475-3081
VL  - 20
IS  - 6
SP  - 834
EP  - 847
PB  - Cambridge Univ. Press
CY  - New York
ER  - 
TY  - JOUR
A1  - Aguado, Felicidad
A1  - Cabalar, Pedro
A1  - Fandinno, Jorge
A1  - Pearce, David
A1  - Perez, Gilberto
A1  - Vidal, Concepcion
T1  - Forgetting auxiliary atoms in forks
JF  - Artificial intelligence
N2  - In this work we tackle the problem of checking strong equivalence of logic programs that may contain local auxiliary atoms, to be removed from their stable models and to be forbidden in any external context. We call this property projective strong equivalence (PSE). It has been recently proved that not any logic program containing auxiliary atoms can be reformulated, under PSE, as another logic program or formula without them – this is known as strongly persistent forgetting. In this paper, we introduce a conservative extension of Equilibrium Logic and its monotonic basis, the logic of Here-and-There, in which we deal with a new connective ‘|’ we call fork. We provide a semantic characterisation of PSE for forks and use it to show that, in this extension, it is always possible to forget auxiliary atoms under strong persistence. We further define when the obtained fork is representable as a regular formula.
KW  - Answer set programming
KW  - Non-monotonic reasoning
KW  - Equilibrium logic
KW  - Denotational semantics
KW  - Forgetting
KW  - Strong equivalence
Y1  - 2019
U6  - https://doi.org/10.1016/j.artint.2019.07.005
SN  - 0004-3702
SN  - 1872-7921
VL  - 275
SP  - 575
EP  - 601
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Cabalar, Pedro
A1  - Fandinno, Jorge
A1  - Schaub, Torsten H.
A1  - Schellhorn, Sebastian
T1  - Gelfond-Zhang aggregates as propositional formulas
JF  - Artificial intelligence
N2  - Answer Set Programming (ASP) has become a popular and widespread paradigm for practical Knowledge Representation thanks to its expressiveness and the available enhancements of its input language. One of such enhancements is the use of aggregates, for which different semantic proposals have been made. In this paper, we show that any ASP aggregate interpreted under Gelfond and Zhang's (GZ) semantics can be replaced (under strong equivalence) by a propositional formula. Restricted to the original GZ syntax, the resulting formula is reducible to a disjunction of conjunctions of literals but the formulation is still applicable even when the syntax is extended to allow for arbitrary formulas (including nested aggregates) in the condition. Once GZ-aggregates are represented as formulas, we establish a formal comparison (in terms of the logic of Here-and-There) to Ferraris' (F) aggregates, which are defined by a different formula translation involving nested implications. In particular, we prove that if we replace an F-aggregate by a GZ-aggregate in a rule head, we do not lose answer sets (although more can be gained). This extends the previously known result that the opposite happens in rule bodies, i.e., replacing a GZ-aggregate by an F-aggregate in the body may yield more answer sets. Finally, we characterize a class of aggregates for which GZ- and F-semantics coincide.
KW  - Aggregates
KW  - Answer Set Programming
Y1  - 2019
U6  - https://doi.org/10.1016/j.artint.2018.10.007
SN  - 0004-3702
SN  - 1872-7921
VL  - 274
SP  - 26
EP  - 43
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Aguado, Felicidad
A1  - Cabalar, Pedro
A1  - Fandiño, Jorge
A1  - Pearce, David
A1  - Perez, Gilberto
A1  - Vidal-Peracho, Concepcion
T1  - Revisiting Explicit Negation in Answer Set Programming
JF  - Theory and practice of logic programming
KW  - Answer set programming
KW  - Non-monotonic reasoning
KW  - Equilibrium logic
KW  - Explicit negation
Y1  - 2019
U6  - https://doi.org/10.1017/S1471068419000267
SN  - 1471-0684
SN  - 1475-3081
VL  - 19
IS  - 5-6
SP  - 908
EP  - 924
PB  - Cambridge Univ. Press
CY  - New York
ER  - 
TY  - JOUR
A1  - Cabalar, Pedro
A1  - Dieguez, Martin
A1  - Schaub, Torsten H.
A1  - Schuhmann, Anna
T1  - Towards metric temporal answer set programming
JF  - Theory and practice of logic programming
N2  - We elaborate upon the theoretical foundations of a metric temporal extension of Answer Set Programming. In analogy to previous extensions of ASP with constructs from Linear Temporal and Dynamic Logic, we accomplish this in the setting of the logic of Here-and-There and its non-monotonic extension, called Equilibrium Logic. More precisely, we develop our logic on the same semantic underpinnings as its predecessors and thus use a simple time domain of bounded time steps. This allows us to compare all variants in a uniform framework and ultimately combine them in a common implementation.
Y1  - 2020
U6  - https://doi.org/10.1017/S1471068420000307
SN  - 1471-0684
SN  - 1475-3081
VL  - 20
IS  - 5
SP  - 783
EP  - 798
PB  - Cambridge Univ. Press
CY  - Cambridge [u.a.]
ER  -