A transition event (or simply event) on a state set $S$ is an element $e = (s_i, s_j) \in (S\times S)$ of a binary relation on state set $S$ that signifies the transition from one state to another. An event $e$ is defined by a condition function $c(s_i)$ which evaluates a Boolean function in state $s_i$ and by an action function $p$ .