cases b <;> simp [← Nat.two_mul]
case f.z
b : Bool
n✝ : ℕ
a✝ : bit b n✝ = n✝ → Bool.xor (decide (0 % 2 = 0)) (decide (bit b n✝ % 2 = 1)) = decide ((0 + bit b n✝) % 2 = 0)
⊢ Bool.xor (decide (0 % 2 = 0)) (decide (bit b n✝ % 2 = 1)) = decide ((0 + bit b n✝) % 2 = 0)
no goals