i + i = j0 ⊦ ∃ i0. (i0 + i0) + 1 = j0 ∨ 2 + i0 + i0 = j0
i + i + 1 = j0 ⊦ ∃ i0. (i0 + i0) + 1 = j0 ∨ 2 + i0 + i0 = j0