def fdiff(self, argindex=1):
        z, m = self.args
        fm = sqrt(1 - m*sin(z)**2)
        if argindex == 1:
            return 1/fm
        elif argindex == 2:
            return (elliptic_e(z, m)/(2*m*(m - 1)) - elliptic_f(z, m)/(2*m) -
                    sin(2*z)/(4*(1 - m)*fm))
        raise ArgumentIndexError(self, argindex)
dataset/ETHPy150Open sympy/sympy/sympy/functions/special/elliptic_integrals.py/elliptic_f.fdiff/swapped operands of `-`