def circular_references(self) -> Set[str]:
        """
        Return the set of recursive (circular) references
        :return:
        """
        rval = set()
        for k in self.grammarelts.keys():
            if k in self.dependency_closure(k):
                rval.add(k)
        return rval
def circular_references ( self ) -> Set [ str ] : rval = set ( ) for k in self . grammarelts . keys ( ) : if k in self . dependency_closure ( k ) : rval . add ( k ) return rval
Return the set of recursive (circular) references
        :return: