1.3 Rule of precedence between superclasses of the same origin
If several superclasses have attributes/methods with the same name and the same
origin, the attribute/method is inherited only once. If the domain of the attribute
has been redefined in any superclass, the attribute with the most specialized domain
is inherited by the subclass. If domains cannot be compared, the attribute is
inherited from the first superclass. For example, SalesStaffClient inherits name and
DOB from both SalesStaff and Client; however, as these attributes are themselves
inherited ultimately from Person, they are inherited only once by SalesStaffClient.