Status and Active States:

Computations are sequences of statuses. A status consists of two components: a set of states in which the computation currently resides (also called ``active states'') and a set of currently present events. At the moment, in our example SUD and P1 are active. Below, we generally mention only subsets of the set of active states; implicitly it is understood that all ancestor states of an active state are also active. The set of present events is . Events provided by the environment are recorded in the event set of the status.