∀ (i : ℤ) (hi : i ≠ 0) (acc k_2 : ℕ) (x_1 : k_2 + 1 ≠ 0) (hk_2 : i.natAbs ≤ k_2 + 1),
  Int.trailingZeros.aux k_2.succ i hi hk_2 acc =
    if h : i % 2 = 0 then Int.trailingZeros.aux k_2 (i / 2) ⋯ ⋯ (acc + 1) else acc