Activator
•SDL differentiates between process definition and process instance
•Defined process activation mechanism
•Receiver process instance
• (1 receiverprocess start
•   ((ackid . nil) (frameid . nil) (self . 1)
•     (sender . nil) (parent . 0) (offspring . nil)
•    ((start …)) nil)
•Correctness property: defined a recognizer for valid instances of a system
• (defthm activate-makes-instance
•   (implies (wf-type S)
•             (wf-instance (activate S) S)))