Central to theories of concurrency is the notion of abstraction. Abstraction from internal actions is the most important tool for system verification. In this paper, we look at abstraction in the framework of the Algebra of Communicating Processes (see BERGSTRA & KLOP [4, 6]). We introduce a hidden step η, and construct a model for the resulting theory ACPη. We briefly look at recursive specifications in this theory, and discuss the relations with Milner's silent step τ.


Baeten, J.C.M, & van Glabbeek, R.J. (1987). Another look at abstraction in process algebra: Extended abstract. In Lecture Notes in Computer Science/Lecture Notes in Artificial Intelligence (pp. 84–94). doi:10.1007/3-540-18088-5_8