The Pyglaf Argumentation Reasoner *

Mario, Alviano
2017 licensed under Creative Commons License CC-BY Technical Communications of the 33rd International Conference on Logic Programming   unpublished
The pyglaf reasoner takes advantage of circumscription to solve computational problems of abstract argumentation frameworks. In fact, many of these problems are reduced to circumscrip-tion by means of linear encodings, and a few others are solved by means of a sequence of calls to an oracle for circumscription. Within pyglaf, Python is used to build the encodings and to control the execution of the external circumscription solver, which extends the SAT solver glucose and implements an algorithm
more » ... ements an algorithm based on unsatisfiable core analysis. 1998 ACM Subject Classification I.2.4 Knowledge Representation Formalisms and Methods 1 Introduction Circumscription [9] is a nonmonotonic logic formalizing common sense reasoning by means of a second order semantics, which essentially enforces to minimize the extension of some predicates. With a little abuse on the definition of circumscription, the minimization can be imposed on a set of literals, so that a set of negative literals can be used to encode a maximization objective function. Since many semantics of abstract argumentation frameworks are based on a preference relation that essentially amount to inclusion relationships, pyglaf (http://alviano.com/software/pyglaf/) uses circumscription as a target language to solve computational problems of abstract argumentation frameworks. pyglaf is implemented in Python and uses circumscriptino [1], a circumscription solver extending the SAT solver glucose [7] with the unsatisfiable core based algorithm one [6] enhanced by reiterated progression shrinking [3], native support for cardinality constraints as in wasp [4, 5, 8], and polyspace model enumeration [2]. Linear reductions are used for all considered semantics. The communication between pyglaf and circum-scriptino is handled in the simplest possible way, that is, via stream processing. In fact, the communication is limited to a single invocation of the circumscription solver. 2 From Argumentation Frameworks to Circumscription Let A be a fixed, countable set of atoms including ⊥. A literal is an atom possibly preceded by the connective ¬. For a literal , let denote its complementary literal, that is, p = ¬p and ¬p = p for all p ∈ A; for a set L of literals, let L be { | ∈ L}. Formulas are defined as *
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