(x+y-4xy)(y-x+4xy)(x+y)(y-x) = (x+y)^2(y-x)^2 = (x^2 + 2xy + y^2)(y^2 - 2xy + x^2= x^2y^2 - 2x^2yx + x^4 + 2x^2y^2 - 4xy^2 + 2xyx + y^4 - 2y^3x + y^2x^= x^4y^2 - 2x^4x + x^6 + 2x^2y^4 - 4x^2y^3 + 2x^3y^2 + y^6 - 2y^5x + y^4x^= x^6y^2 - 2x^5y + x^7 + 2x^2y^4 - 4x^2y^3 + 2x^3y^2 + y^6 - 2y^5x + y^4*x^2
(x+y-4xy)(y-x+4xy)(x+y)(y-x) = (x+y)^2(y-x)^2 = (x^2 + 2xy + y^2)(y^2 - 2xy + x^2
= x^2y^2 - 2x^2yx + x^4 + 2x^2y^2 - 4xy^2 + 2xyx + y^4 - 2y^3x + y^2x^
= x^4y^2 - 2x^4x + x^6 + 2x^2y^4 - 4x^2y^3 + 2x^3y^2 + y^6 - 2y^5x + y^4x^
= x^6y^2 - 2x^5y + x^7 + 2x^2y^4 - 4x^2y^3 + 2x^3y^2 + y^6 - 2y^5x + y^4*x^2