code: def external_incompatibilities(self):  # type: () -> Generator[Incompatibility]
          
          if isinstance(self._cause, ConflictCause):
              cause = self._cause  # type: ConflictCause
              for incompatibility in cause.conflict.external_incompatibilities:
                  yield incompatibility
  
              for incompatibility in cause.other.external_incompatibilities:
                  yield incompatibility
          else:
              yield self
docs: Returns all external incompatibilities in this incompatibility's
          derivation graph.