i1 < i0, j0 < j1, i + i0 < j + j0, i + j1 < j + j0 ⊦ i + i1 < j + j1
i1 < i0, j0 < j1, i + i0 < j + j0 ⊦ i + i1 < j + j1, i + j1 < j + j0
Used formulas: i + j1 < j + j0