rw [size_bit]
case f
b : Bool
n : ℕ
hb : n = 0 → b = true
ih : size n ≤ n
⊢ size (bit b n) ≤ bit b n
case f
b : Bool
n : ℕ
hb : n = 0 → b = true
ih : size n ≤ n
⊢ succ (size n) ≤ bit b n

case f
b : Bool
n : ℕ
hb : n = 0 → b = true
ih : size n ≤ n
⊢ bit b n ≠ 0