Towards Complete Reasoning about Axiomatic Specifications

To support verification of expressive properties of functional programs, we consider algebraic style specifications that may relate multiple user-defined functions, and compare multiple invocations of a function for different arguments. We present decision procedures for reasoning about such universally quantified properties of functional programs, using local theory extension methodology. We establish new classes of universally quantified formulas whose satisfiability can be checked in a complete way by finite quantifier instantiation. These classes include single-invocation axioms that generalize standard function contracts, but also certain many-invocation axioms, specifying that functions satisfy congruence, injectivity, or monotonicity with respect to abstraction functions, as well as conjunctions of some of these properties. These many-invocation axioms can specify correctness of abstract data type implementations as well as certain information-flow properties. We also present a decidability-preserving construction that enables the same function to be specified using different classes of decidable specifications on different partitions of its domain.