The object 0 acts as a zero for both sum and multiplication in process algebra. The constant δ, representing deadlock or inaction, is only a left zero for multiplication. We will call 0 predictable failure.

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doi.org/10.1007/BFb0039053
International Conference on Concurrency Theory

Baeten, J.& Bergstra, J. (1990). Process algebra with a zero object. Lecture Notes in Computer Science/Lecture Notes in Artificial Intelligence, 83–98.https://doi.org/10.1007/BFb0039053