⊦ i * j ≤ 0 ↔ i = 0 ∨ j = 0 ∨ 0 < i ∧ j < 0 ∨ i < 0 ∧ 0 < j
Used simplifier rules: lels-02: ⊦ i ≠ j → (i ≤ j ↔ i < j); from specification int-abs