⊦ ri = rj ↔ ri.num = rj.num ∧ ri.denom = rj.denom
j < 0 ⊦ rational(i, j).num = rational(~ i, ~ j).num ∧ rational(i, j).denom = rational(~ i, ~ j).denom
Used terms: rational(~ i, ~ j), rational(i, j)