|x + y - 1|≤3
-3 ≤ x + y - 1 ≤ 3
-2 ≤ x + y ≤ 4
-4 ≤ -(x + y) ≤ 2
-4 + 2x ≤ x - y ≤ 2 + 2x
x≤0,x - y ≤ 2