3.2 Rule for removing superclasses
If a class C has a single superclass Cs, and Cs is deleted from the list of superclasses
of C, then C becomes a direct subclass of each direct superclass of Cs. The ordering
of the new superclasses of C is the same as that of the superclasses of Cs.
For example, if we were to delete the superclass Staff, the subclasses Manager and
SalesStaff would then become direct subclasses of Person.