case zero =>
  conv => lhs; dsimp [bitmask.aux, UInt.getBit]; rw [toNat_zero]
  simp [bitmask.aux, Nat.not_lt_zero i]
α : Type
inst✝¹ : (n : Nat) → OfNat α n
inst✝ : UInt α
n : α
i : Nat
hn : toNat n < length α
hk : Nat.zero ≤ length α
⊢ UInt.getBit (bitmask.aux n Nat.zero) i = (decide (i < Nat.zero) && Nat.getBit i (toNat n))
no goals