| j ≠ 0 ∧ j0 ≠ 0, 0 < j, 0 < j0, 0 < j1 ⊦ rational(i * i0, j * j0) * rational(i1, j1) = rational(i, j) * rational(i0, j0) * rational(i1, j1) |
0 < j1, 0 < j0, 0 < j ⊦ j = 0, j0 = 0, rational(i * i0, j * j0) * rational(i1, j1) = rational(i, j) * rational(i0, j0) * rational(i1, j1)