Nonexpressibility of fairness and signaling

Expressiveness results for indeterminate data flow primitives are established. Choice primitives with three differing fairness assumptions are considered, and it is shown that they are strictly inequivalent in expressive power. It is also shown that the ability to announce choices enhances the expressive power of two of the primitives. These results are proved using a very crude semantics and will thus apply in any reasonable theory of process equivalence