(self, number_cls)
Return an interval with number_cls endpoints
        that contains the value of NumberSymbol.
        If not implemented, then return None.
Return an interval with number_cls endpoints
        that contains the value of NumberSymbol.
        If not implemented, then return None.
Return an interval with number_cls endpoints that contains the value of NumberSymbol . If not implemented then return None .
def approximation(self, number_cls):
        """ Return an interval with number_cls endpoints
        that contains the value of NumberSymbol.
        If not implemented, then return None.
        """
def approximation ( self , number_cls ) :