(x²-y)²-(2y-2)²=(x²-y+2y-2)(x²-y-2y+2)=(x²+y-2)(x²-3y+2);
(a²-2b)²-(1-2b)²=(a²-2b+1-2b)(a²-2b-1+2b)=(a²-4b+1)(a+1)(a-1)