enduser/Modal-Transition-Systems.md

+# 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).
+```
+
+# End