code: def is_opposite(self, ns1, id1, ns2, id2):
          
          u1 = self.get_uri(ns1, id1)
          u2 = self.get_uri(ns2, id2)
          t1 = rdflib.term.URIRef(u1)
          t2 = rdflib.term.URIRef(u2)
  
          rel = rdflib.term.URIRef(self.relations_prefix + 'is_opposite')
          to = self.graph.objects(t1, rel)
          if t2 in to:
              return True
          return False
docs: Return True if two entities are in an "is_opposite" relationship
  
          Parameters
          ----------
          ns1 : str
              Namespace code for an entity.
          id1 : str
              URI for an entity.
          ns2 : str
              Namespace code for an entity.
          id2 : str
              URI for an entity.
  
          Returns
          -------
          bool
              True if t1 has an "is_opposite" relationship with t2.