b2i(by) = ub2i(by0), 0 ≤ ub2i(by0) ⊦ by = by0
Used simplifier rules: ubyte-pos: ⊦ 0 ≤ b2i(by) → ub2i(by) = b2i(by);% ⊦ i ≤ j ∧ 0 ≤ i → 0 ≤ j; (forward)% ⊦ ¬ i < j ↔ j ≤ i;