rw [bitwise_div_two]
case hdiv
k : Nat
h_ind : ∀ (n : Nat), n &&& 2 ^ k - 1 = n % 2 ^ k
n : Nat
⊢ bitwise and n (2 * 2 ^ k - 1) / 2 = n % (2 * 2 ^ k) / 2
case hdiv
k : Nat
h_ind : ∀ (n : Nat), n &&& 2 ^ k - 1 = n % 2 ^ k
n : Nat
⊢ bitwise and (n / 2) ((2 * 2 ^ k - 1) / 2) = n % (2 * 2 ^ k) / 2