Axioms for Asynchronous Processes

From classical computability theory to modern programming language design, the mathematical concept of function has dominated the perception of sequential computation. But as soon as the authors venture into the realm of concurrent interaction, it is well understood that this concept has to be abandoned. What are they to replace it with? This question is considered too general to admit a definitive answer. If they want such an answer, they must be willing to narrow the scope, and impose some constraint on the form of concurrent interaction that they choose to consider. Here, they derive such a constraint solely from the intuitive notion of asynchrony.