ub2i(by) = 0, 0 < b2i(by) ⊦
Used simplifier rules: ⊦ i < j ∧ 0 ≤ i → 0 < j; (forward)% ⊦ i < j → ¬ j < i;% ⊦ ¬ i < j → (i ≠ j ↔ j < i);