Approximating unity

Abstract

A framework for the stepwise refinement of UNITY programs with local variables is proposed. It is centered around two preorders. The first one compares program components with respect to a given context. Aside from being context-sensitive, this order also allows the introduction of local variables. The second preorder compares program contexts with respect to their discriminating power. Using these two relations, program refinement arises as a form of assumption/commitment reasoning. An example illustrates the use of the framework and presents some proof rules. The simple syntactic and semantic structure of UNITY allows for a natural game-theoretic characterization of the preorders used in the framework.