(i1 + 1) + j = (i1 + 1) + i0, i1 + 1 + j = i1 + 1 + i0 → 1 + j = 1 + i0, ∀ j, i0. i1 + j = i1 + i0 → j = i0 ⊦ j = i0
Used terms: 1 + j, 1 + i0