(self)
return self.function.is_zero
A Sum is only zero if its function is zero or if all terms
        cancel out. This only answers whether the summand zero.
A Sum is only zero if its function is zero or if all terms
        cancel out. This only answers whether the summand zero.
A Sum is only zero if its function is zero or if all terms cancel out . This only answers whether the summand zero .
def is_zero(self):
        """A Sum is only zero if its function is zero or if all terms
        cancel out. This only answers whether the summand zero."""

        return self.function.is_zero
def is_zero ( self ) : return self . function . is_zero