Javier Leach

Constraint Logic Programming with Hereditary Harrop formulas

Constraint Logic Programming (CLP) and Hereditary Harrop formulas (HH) are two well known ways to enhance the expressivity of Horn clauses. In this paper, we present a novel combination of these two approaches. We show how to enrich the syntax and proof theory of HH with the help of a given constraint system, in such a way that the key property of HH as a logic programming language (namely, the existence of uniform proofs) is preserved. We also present a procedure for goal solving, showing its soundness and completeness for computing answer constraints. As a consequence of this result, we obtain a new strong completeness theorem for CLP that avoids the need to build disjunctions of computed answers, as well as a more abstract formulation of a known completeness theorem for HH.

A logic programming approach to the verification of functional-logic programs

We address in this paper the question of how to verify program properties in modern functional logic languages, where it is allowed the presence of non-deterministic functions with call-time choice semantics. The main problem to face is that for such kind of programs equational reasoning is not valid. We develop some logical conceptual tools providing sound reasoning mechanisms for these programs, in particular for proving properties valid in the initial model of a program. We show how CRWL, a well known logical framework for functional logic programming, can be easily mapped into logic programming, and we use this mapping as a starting point of our work. We explore then how to prove properties of the resulting logic programming translation by means of different existing interactive proof assistants, and afterwards we give some proposals trying to overcome the limitations of the approach, specially with respect to its theoretical strength.

A Higher-Order Logic Programming Language with Constraints

We present a framework for the combination of Constraint Logic Programming (tiCLP) and higher-order Hereditary Harrop Formulas (tihoHH). Our aim is to improve the expressiveness of traditional Logic Programming with the benefits of both fields: tiCLP and tihoHH. The result is denoted higher-order Hereditary Harrop Formulas with Constraints (hoHH(C)). The syntax of hoHH is introduced using lambda-terms and is enriched with a basic constraint system. Then an intuitionistic sequent calculus is defined for this combined logic, that preserves the property of an abstract logic programming language. In addition, a sound and complete procedure for goal solving is presented as a transformation system that explains the operational semantics.

Reasoning with Preorders and Dynamic Sorts Using Free Variable Tableaux

In this paper we present a three valued many sorted logic for dealing with preorders, incorporating subsort relations into the syntax of the language, and where formulas taking the third boolean value as interpretation contain a term or a predicate which is not well-sorted w.r.t. the signature. For this logic a ground tableau-based deduction method and a free variable extension version are proposed, proving their completeness.

Tableau Methods for a Logic with Term Declarations

We study free variable tableau methods for logics with term declarations. We show how to define a substitutivity rule preserving the soundness of the tableaux and we prove that some other attempts lead to unsound systems. Based on this rule, we define a sound and complete free variable tableau system and we show how to restrict its application to close branches by defining a sorted unification calculus.

Foundations of a theorem prover for functional and mathematical uses

ABSTRACT A computational logic, PLPR (Predicate Logic using Polymorphism and Recursion) is presented. Actually this logic is the object language of an automated deduction system designed as a tool for proving mathematical theorems as well as specify and verify properties of functional programs. A useful denotationl semantics and two general deduction methods for PLPR are defined. The first one is a tableau algorithm proved to be complete and also used as a guideline for building complete calculi. The second is a sound and complete natural deduction system. Moreover a fixed point induction rule is introduced for formulas called continuous. The strategies for mechanizing the proofs of the final automated system are based on the previous deduction methods. As the examples of the use of the system show, the implemented theorem prover outperforms humans to a certain extent, retaining logic and calculi generality.

Free Variable Tableaux for a Logic with Term Declarations

We study free variable tableau methods for logics with term declarations. We show how to define a substitutivity rule preserving the soundness of the tableaux and we prove that some other attempts lead to unsound systems. Based on this rule, we define a sound and complete free variable tableau system and we show how to restrict its application to close branches by defining a sorted unification calculus.

Free Variable Tableaux for a Many Sorted Logic with Preorders

We propose a sound and complete free variable semantic tableau method for handling many-sorted preorders in a first order logic, where functions and predicates behave monotonically or antimonotonically. We formulate additional expansion tableau rules as a more efficient alternative to adding the axioms characterizing a preordered structure. Completeness of the system is proved in detail. Examples and applications are introduced.

Public and Personal Causations of Creditions

In this chapter, I classify the causes of the processes of believing (creditions) into two types: the causes of public processes, and the causes of personal processes. Public creditons are so characterized because they mean the same for everyone. Personal creditions are so characterized because they can have different meanings for different people. Each causal type of a credition corresponds to a kind of language. We use a language that tends to be formal and objective to express the causes of public creditions and we use a symbolic language to express the causes of the processes of personal creditions.