- forth letter (if present)
-c: proper single step (successor)
+c: proper single step (general) (successor)
e: reflexive transitive closure to normal form (evaluation)
g: proper multiple step (general) (greater)
p: non-reflexive transitive closure (plus)
q: reflexive closure (question)
r: proper multiple step (restricted) (restricted)
s: reflexive transitive closure (star)
+u: proper single step (restricted) (unit)