A proof of the Kahn principle for input/output automata

We use input/output automata to define a simple and general model of networks of concurrently executing, nondeterministic processes that communicate through unidirectional, named ports. A notion of the input/output relation computed by a process is defined, and determinate processes are defined to be processes whose input/output relations are single-valued. We show that determinate processes compute continuous functions, and that networks of determinate processes obey Kahn's fixed-point principle. Although these results are already known, our contribution lies in the fact that the input/output automata model yields extremely simple proofs of them (the simplest we have seen), in spite of its generality.