Here's something Joe Armstrong's PhD thesis does reference in the context of message passing: "4.5 Programming Notations Based on Message Passing" p33 "Concep

Here's something Joe Armstrong's PhD thesis does reference in the context of message passing: "4.5 Programming Notations Based on Message Passing" p33 "Concepts and Notations for Concurrent Programming", Gregory R. Andrews and Fred B. Scheider, Computing Surveys 15(1) March 1983, pp 3 - 43 [pdf] https://www.cs.cornell.edu/fbs/publications/LangSurv.pdf https://www.cs.cornell.edu/fbs/publications/LangSurv.pdf