Modelling angelic and demonic nondeterminism with multirelations

This paper presents an introduction to a calculus of binary multirelations, which can model both angelic and demonic kinds of non-determinism. The isomorphism between up-closed multirelations and monotonic predicate transformers allows a different view of program transformation, and program transformation calculations using multirelations are easier to perform in some circumstances. Multirelations are illustrated by modelling both kinds of nondeterministic behaviour in games and resource-sharing protocols.