Variant-Based Decidable Satisfiability in Initial Algebras with Predicates

TL;DR

This paper extends variant-based satisfiability decision procedures to handle initial algebras with user-definable predicates, broadening the applicability of theory-generic decision methods beyond data structures.

Contribution

It introduces a new theory-generic satisfiability procedure that accommodates user-definable predicates, along with a prototype implementation extending existing variant-based methods.

Findings

The procedure applies to a wide range of theories with predicates.

It successfully extends variant satisfiability to more complex theories.

Prototype implementation demonstrates practical feasibility.

Abstract

Decision procedures can be either theory-specific, e.g., Presburger arithmetic, or theory-generic, applying to an infinite number of user-definable theories. Variant satisfiability is a theory-generic procedure for quantifier-free satisfiability in the initial algebra of an order-sorted equational theory $({\Sigma},E \cup B)$ under two conditions: (i) $E \cup B$ has the finite variant property and $B$ has a finitary unification algorithm; and (ii) $({\Sigma},E \cup B)$ protects a constructor subtheory $({\Omega},E_{\Omega} \cup B_{\Omega})$ that is OS-compact. These conditions apply to many user-definable theories, but have a main limitation: they apply well to data structures, but often do not hold for user-definable predicates on such data structures. We present a theory-generic satisfiability decision procedure, and a prototype implementation, extending variant-based satisfiability to initial algebras with user-definable predicates under fairly general conditions.