Springer
doi.org/10.1007/3-540-15670-4_4
Seminar on Concurrency
Specification and Analysis of Embedded Systems

Bergstra, J., Klop, J. W.& Tucker, J. (1984). Process algebra with asynchronous communication mechanisms. Lecture Notes in Computer Science, 76–95.https://doi.org/10.1007/3-540-15670-4_4