Interpolation in local theory extensions

In this paper we study interpolation in local extensions of a base theory. We identify situations in which it is possible to obtain interpolants in a hierarchical manner, by using a prover and a procedure for generating interpolants in the base theory as black-boxes. We present several examples of theory extensions in which interpolants can be computed this way, and discuss applications in verification, knowledge representation, and modular reasoning in combinations of local theories.Comment: 31 pages, 1 figur

Complete Sets of Reductions Modulo A Class of Equational Theories which Generate Infinite Congruence Classes

In this paper we present a generalization of the Knuth-Bendix procedure for generating a complete set of reductions modulo an equational theory. Previous such completion procedures have been restricted to equational theories which generate finite congruence classes. The distinguishing feature of this work is that we are able to generate complete sets of reductions for some equational theories which generate infinite congruence classes. In particular, we are able to handle the class of equational theories which contain the associative, commutative, and identity laws for one or more operators. We first generalize the notion of rewriting modulo an equational theory to include a special form of conditional reduction. We are able to show that this conditional rewriting relation restores the finite termination property which is often lost when rewriting in the presence of infinite congruence classes. We then develop Church-Rosser tests based on the conditional rewriting relation and set forth a completion procedure incorporating these tests. Finally, we describe a computer program which implements the theory and give the results of several experiments using the program

Median based calculus for lattice polynomials and monotone Boolean functions

International audienceIn this document, we consider a median-based calculus for efficiently representing polynomial functions over distributive lattices. We extend an equational specification of median forms from the domain of Boolean functions to the domain of lattice polynomials. We show that it is sound and complete, and we illustrate its usefulness when simplifying median formulas algebraically. Furthermore, we propose a definition of median normal forms (MNF), that are thought of as minimal median formulas with respect to a structural ordering of expressions. We also investigate related complexity issues and show that the problem of deciding whether a formula is in MNF is in Σ^P_2. Moreover, we explore polynomial approximations of solutions to this problem through a sound term rewriting system extracted from the proposed equational specification