⊦ 0 < j ∧ 0 < i1 → rational(i1 * i, i1 * j) = rational(i, j)
¬(0 < j ∧ 0 < i1), 0 < j ⊦ rational(i1 * i, i1 * j) = rational(i, j), i1 = 0
Used terms: j, i, i1