Used simplifier rules: ⊦ i ≤ j ↔ ¬ j < i; (ss)% ⊦ 0 < j → abs(j) = j; (s)% ⊦ i < j → ¬ j < i; (s)% ⊦ i ≤ 0 ∧ 0 ≤ j → i ≤ j; (s)% ⊦ i < j ↔ ¬ j ≤ i; (ss)