-If $C$ has a proper superclass $B$, then $B$ is not allowed to have $C$ has a
-direct superclass. In different terms, if we construct a graph, whose
-vertices are classes, and draw an edge from each class to each of its direct
-superclasses, then this graph must be acyclic. In yet other terms, the `is a
-superclass of' relation is a partial order on classes.
+If $C$ has a proper superclass $B$, then $B$ must not have $C$ as a direct
+superclass. In different terms, if we construct a graph, whose vertices are
+classes, and draw an edge from each class to each of its direct superclasses,
+then this graph must be acyclic. In yet other terms, the `is a superclass
+of' relation is a partial order on classes.