Asynchrony and the pi-calculus, INRIA Research Report 1702 (May 1992).

Abstract:
We introduce an asynchronous version of Milner's pi-calculus, based on the idea that the messages are elementary processes that can be sent without any sequencing constraint. We show that this simple message passing discipline, together with the restriction construct making a name private for an agent, is enough to encode the synchronous communication of the pi-calculus.
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