I am getting an error with the code below. Please advise how I can do this. Thanks
sage: K.<x> = QQ[]
sage: _.<y> = K[]
sage: K.<y> = K.extension(y^2 - x^3 - x)
sage: I = Ideal(x, y)
sage: I
Ideal (x, y) of Univariate Quotient Polynomial Ring in y over Univariate Polynomial Ring in x over Rational Field with modulus y^2 - x^3 - x
sage: x - y^2 + x^3 in I
...
NotImplementedError:
