（x^2+y^2-2x+1)^2-(4y-4xy)(x^2-y^2-2x+1)

(x^2+y^2-2x+1)^2-(4y-4xy)(x^2-y^2-2x+1)
=(x^2+y^2-2x+1)^2-4y(1-x)(x^2-y^2-2x+1)
=[(x-1)^2+y^2]^2+4y(x-1)[(x-1)^2-y^2]
设：a=x-1,b=y
原式=(a^2+b^2)^2+4ab(a^2-b^2)
=(a^2+b^2)^2+4ab(a^2+b^2-2b^2)
=(a^2+b^2)^2+4ab(a^2+b^2)+4a^2b^2-4a^2b^2-8ab^3)
=(a^2+b^2+2ab)^2-4ab^2(a+2b)
=[a(a+2b)]^2+2ab^2(a+2b)+b^4-4ab^2(a+2b)
=[a(a+2b)-b^2]^2
将：a=x-1,b=y代入
原式=[(x-1)(x+2y-1)-y^2]^2