An extensional treatment of dataflow deadlock

We discuss deadlock in reference to a simple equation data-flow language, and devise a test (the cycle sum test) which is applied to the dependency graph of a Program we use Kahn's extensional semantics of data-flow and give a purely extensional (non operational) proof that no program passing the cycle sum test can ever deadlock. The proof is based on the notions of size (length) and completeness in the domain of histories, and should extend to a much widen context