⊦ fillsgn(n, int2bits(j)).first ↔ ¬ 0 ≤ j
Used simplifier rules: int2bits-first-02: ⊦ int2bits(j).first ↔ j < 0;% ⊦ ¬ i ≤ j ↔ j < i;% ⊦ ¬ i < j ↔ j ≤ i;