Ordered Resolution with Straight Dismatching Constraints

International audienceWe present a sound and complete ordered resolution calculus for first-order clauses with straight dismatching constraints. The extended clause language is motivated by our first-order theorem proving approach through approximation and refinement. Using a clause language with straight dismatching constraints, single refinement steps do not result in a worst-case quadratic blowup in the number of clauses anymore. The refinement steps can now be represented by replacing one input clause with two equivalent clauses. We show soundness and completeness of ordered resolution with straight dismatching constraints. All needed operations on straight dismatching constraints take linear or linear logarithmic time in the size of the constraint

Decidability of the Monadic Shallow Linear First-Order Fragment with Straight Dismatching Constraints

The monadic shallow linear Horn fragment is well-known to be decidable and has many application, e.g., in security protocol analysis, tree automata, or abstraction refinement. It was a long standing open problem how to extend the fragment to the non-Horn case, preserving decidability, that would, e.g., enable to express non-determinism in protocols. We prove decidability of the non-Horn monadic shallow linear fragment via ordered resolution further extended with dismatching constraints and discuss some applications of the new decidable fragment.Comment: 29 pages, long version of CADE-26 pape

On the Expressivity and Applicability of Model Representation Formalisms

A number of first-order calculi employ an explicit model representation formalism for automated reasoning and for detecting satisfiability. Many of these formalisms can represent infinite Herbrand models. The first-order fragment of monadic, shallow, linear, Horn (MSLH) clauses, is such a formalism used in the approximation refinement calculus. Our first result is a finite model property for MSLH clause sets. Therefore, MSLH clause sets cannot represent models of clause sets with inherently infinite models. Through a translation to tree automata, we further show that this limitation also applies to the linear fragments of implicit generalizations, which is the formalism used in the model-evolution calculus, to atoms with disequality constraints, the formalisms used in the non-redundant clause learning calculus (NRCL), and to atoms with membership constraints, a formalism used for example in decision procedures for algebraic data types. Although these formalisms cannot represent models of clause sets with inherently infinite models, through an additional approximation step they can. This is our second main result. For clause sets including the definition of an equivalence relation with the help of an additional, novel approximation, called reflexive relation splitting, the approximation refinement calculus can automatically show satisfiability through the MSLH clause set formalism

On the Expressivity and Applicability of Model Representation Formalisms

A number of first-order calculi employ an explicit model representation formalism for automated reasoning and for detecting satisfiability. Many of these formalisms can represent infinite Herbrand models. The first-order fragment of monadic, shallow, linear, Horn (MSLH) clauses, is such a formalism used in the approximation refinement calculus. Our first result is a finite model property for MSLH clause sets. Therefore, MSLH clause sets cannot represent models of clause sets with inherently infinite models. Through a translation to tree automata, we further show that this limitation also applies to the linear fragments of implicit generalizations, which is the formalism used in the model-evolution calculus, to atoms with disequality constraints, the formalisms used in the non-redundant clause learning calculus (NRCL), and to atoms with membership constraints, a formalism used for example in decision procedures for algebraic data types. Although these formalisms cannot represent models of clause sets with inherently infinite models, through an additional approximation step they can. This is our second main result. For clause sets including the definition of an equivalence relation with the help of an additional, novel approximation, called reflexive relation splitting, the approximation refinement calculus can automatically show satisfiability through the MSLH clause set formalism.Comment: 15 page

{SPASS-AR}: {A} First-Order Theorem Prover Based on Approximation-Refinement into the Monadic Shallow Linear Fragment

International audienceWe introduce FO-AR, an approximation-refinement approach for first-order theorem proving based on counterexample-guided abstraction refinement. A given first-order clause set N is transformed into an over-approximation N in a decidable first-order fragment. That means if N is satisfiable so is N. However, if N is unsatisfiable, then the approximation provides a lifting terminology for the found refutation which is step-wise transformed into a proof of unsatisfiability for N. If this fails, the cause is analyzed to refine the original clause set such that the found refutation is ruled out for the future and the procedure repeats. The target fragment of the transformation is the monadic shallow linear fragment with straight dismatching constraints, which we prove to be decidable via ordered resolution with selection. We further discuss practical aspects of SPASS-AR, a first-order theorem prover implementing FO-AR. We focus in particularly on effective algorithms for lifting and refinement