Correctness and Refinement of Dually Nondeterministic Programs

In this paper we extend different reasoning methods from traditional (demonic) programs to programs with both demonic and angelic nondeterminism. In particular, we discuss correctness proofs, and refinement of programs while reducing angelic nondeterminism (into demonic nondeterminism or determinism). As expected, reducing angelic nondeterminism is generally not a refinement; however, when context is taken into consideration, it can result in refinement. We also show how correctness proofs can be used to implement a winning strategy for the angel (when such a strategy exists). TUCS Laboratory Learning and Reasoning Laboratory