Modal Transition Systems
Modal transition systems (MTS) can be modelled by using a question mark (?) on event labels.
A = (a -> b? -> A | a? -> A).
Abstract keyword
The abstract keyword builds an MTS from a FSP process adding to each state maybe transitions on labels that are not enabled in the original process. It can be applied both to sequential and composite processes.
abstract A = (a -> b -> A | a->STOP | b->END).
B = (a -> b -> B | b? -> B).
abstract ||COMP = (B).