Follow coreference relationships to get full related graph.

        This differs from ``get_related_coref_relationships`` in that
        it returns a flat list of all identifiers found through the
        coreference layer of indirection.

        :rtype: list of identifiers

def get_related_flat(self, content_id, min_strength=None):
        '''Follow coreference relationships to get full related graph.

        This differs from ``get_related_coref_relationships`` in that
        it returns a flat list of all identifiers found through the
        coreference layer of indirection.

        :rtype: list of identifiers
        '''
        rel_id_to_idents = self.get_related_coref_relationships(
            content_id, min_strength=min_strength)
        flat_list = []
        for val in rel_id_to_idents.values():
            flat_list.extend(val)
        return flat_list