Duplication of constants in process algebra

The constant 0 (or !, nil ) has different roles in process algebra: on the one hand, it serves as the identity element of alternative composition, on the other hand, it stands for a blocked atomic action or for livelock. When extensions with timing are considered, these roles diverge. We argue that it is better to use two separate constants ¿0 and 0 for the different usages. With respect to the termination constant 1 (or , skip), the situation is comparable: on the one hand, it serves as the identity element of sequential composition, on the other hand, it serves as the identity element of parallel composition, and stands for a skipped atomic action. We have separate constants ¿1 and 1 for the different usages