+ #alt20# super SSet
+end
+
+# A subset can inherit anything except a subset, and has only one direct parent.
+
+subset SSetI
+ super IC
+ # TODO: super AC
+ # TODO: super CC
+ # TODO: super EnC
+ # TODO: super ExC
+ # TODO: super SSet
+end
+
+subset SSetA
+ super AC
+end
+
+subset SSetC
+ super CC
+end
+
+subset SSetEn
+ super EnC
+end
+
+subset SSetEx
+ super ExC