y^5 + y^4 - y^4 + y^3 - y^3 + y^3 - y^2 + y^2 + y + 1 =
y^3 ( y^2 + y + 1) - y^2 ( y^2 + y + 1) + y^2 + y + 1 =
( y^2 + y + 1) (y^3 - y^2 + 1)
y^5 + y^4 - y^4 + y^3 - y^3 + y^3 - y^2 + y^2 + y + 1 =
y^3 ( y^2 + y + 1) - y^2 ( y^2 + y + 1) + y^2 + y + 1 =
( y^2 + y + 1) (y^3 - y^2 + 1)