>>21
incorrect, (mod 2).
x - y = x + y
if x = y,
0 = x + y => 0 = 2x, in mod 2 that's 0 = 0
1 4
-3
5
if x != y
x - y = z
if z is even, both x and y are either odd or even, which means in mod2 = 0, their difference would be even as well, 0 = 0
If z is odd, either x or y is what the other is not (odd/even), so 1 = 1