def reduction(g):
    F = g.parent().base()
    x, y = g.parent().gens()
    Rxy.<x, y> = PolynomialRing(F, 2)
    Fxy = FractionField(Rxy)
    Rx.<x> = PolynomialRing(F)
    Fx = FractionField(Rx)
    FxRy.<y> = PolynomialRing(Fx)
    g = Fxy(g)
    g1 = g.numerator()
    g2 = g.denominator()
    print('aa', FxRy(g2))
    
    
F = GF(3).algebraic_closure()
R.<x, y> = PolynomialRing(F, 2)
g = x
reduction(g)