def evolute(self, x='x', y='y'):
        """The equation of evolute of the ellipse.

        Parameters
        ==========

        x : str, optional
            Label for the x-axis. Default value is 'x'.
        y : str, optional
            Label for the y-axis. Default value is 'y'.

        Returns
        =======

        equation : sympy expression

        Examples
        ========

        >>> from sympy import Point, Ellipse
        >>> e1 = Ellipse(Point(1, 0), 3, 2)
        >>> e1.evolute()
        2**(2/3)*y**(2/3) + (3*x - 3)**(2/3) - 5**(2/3)
        """
        if len(self.args) != 3:
            raise NotImplementedError('Evolute of arbitrary Ellipse is not supported.')
        x = _symbol(x)
        y = _symbol(y)
        t1 = (self.hradius*(x - self.center.x))**Rational(2, 3)
        t2 = (self.vradius*(self.center.y - y))**Rational(2, 3)
        return t1 + t2 - (self.hradius**2 - self.vradius**2)**Rational(2, 3)
dataset/ETHPy150Open sympy/sympy/sympy/geometry/ellipse.py/Ellipse.evolute/swapped operands of `-`