⊦ ∃ i, j. ri = rational(i, j) ∧ 0 < j
∃ i, j. ri0 = rational(i, j) ∧ 0 < j, 0 < j ⊦ ri0 = rational(i, j) - rj ↔ rational(i, j) = ri0 + rj
Used terms: ri0