§2.1.2.(a) No role of the same team

The base class of any role class must not be a role of the same team.
It is also not allowed to declare a role class of the same name as a base class bound to this or another role of the enclosing team, if that base class is given with its simple name and resolved using a regular import. Put differently, a base class mentioned after playedBy may not be shadowed by any role class of the enclosing team.
Base imports as defined below (§2.1.2.(d)) relax this rule by allowing to import a class as a base class only. In that case no shadowing occurs since the scopes for base classes and roles are disjoint.