F1 = {x^2 y - y + x^2 = 1, x y + x = 1, x y^3 + y^3 + y = 2}
F2 = {x y^2 -y^2 + x -1, x^3 + x^2, y^2 - y}
F3 = {x y^3 - y^2 -x +1, x y^2 - y, x^3 -x^2 -x +1}
F4 = {x^2 + y^2 -1, 3 x y - 1}
F5 = {x^2 + y^2 -1, 3 x y - 1, x - y -1}
Up to Aufgabe 3