code: def isa(self, ns1, id1, ns2, id2):
          
          rel_fun = lambda node, graph: self.isa_objects(node)
          return self.directly_or_indirectly_related(ns1, id1, ns2, id2,
                                                     self.isa_closure,
                                                     rel_fun)
docs: Return True if one entity has an "isa" relationship to another.
  
          Parameters
          ----------
          ns1 : str
              Namespace code for an entity.
          id1 : string
              URI for an entity.
          ns2 : str
              Namespace code for an entity.
          id2 : str
              URI for an entity.
  
          Returns
          -------
          bool
              True if t1 has an "isa" relationship with t2, either directly or
              through a series of intermediates; False otherwise.