Used simplifier rules: ⊦ i +1 = i + 1; (s)% ⊦ i = ~1 ↔ i +1 = 0; (s)% ⊦ i ≠ 0 ∧ i ≠ 1 → (abs(i) ≤ 1 ↔ i = ~1); (s)