Used simplifier rules: add-a: ⊦ i + j + i0 = (i + j) + i0;%add-c: ⊦ i + j = j + i;%zero-05: ⊦ 0 < i ∧ ¬ j < 0 → 0 ≠ i + j;% ⊦ ¬ i < j → (i = j ↔ ¬ j < i); (ss)