#### §2.1.(c) Covariant refinement

An explicit sub-role (sub-class using `extends`) can refine the `playedBy` relation to a more specific base class (this is the basis for smart lifting (§2.3.3)).
If a role class inherits several `playedBy` relations from its super-class and its super-interfaces, there must be a most specific base-class among these relations, which is conform to all other base-classes. This most specific base-class is the base-class of the current role.