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.

Deadlock, Failure, Inaction, Process algebra, Zero
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International Conference on Concurrency Theory

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