code: def _get_all_relationships(self):
          
          relationships_all = set()
          for goterm in self.go2obj.values():
              if goterm.relationship:
                  relationships_all.update(goterm.relationship)
              if goterm.relationship_rev:
                  relationships_all.update(goterm.relationship_rev)
          return relationships_all
docs: Return all relationships seen in GO Dag subset.