apply round_eq_of_trunc_eq npos hfaithful₀
case inr.inr.inr.round_eq
round : ℕ → ℕ
n a b : ℕ
npos : 0 < n
hfaithful₀ : faithful₀ n round
hfaithful₁ : faithful₁ n round
hcorrect₀ : correct₀ n round
hfa : trunc n a = a
hfb : trunc n b = b
hba : b ≤ a
no_uflow : a - b ≥ 2 ^ n
bpos : b > 0
le_two_mul : 2 * b ≥ a
⊢ round (a - b) = a - b
case inr.inr.inr.round_eq
round : ℕ → ℕ
n a b : ℕ
npos : 0 < n
hfaithful₀ : faithful₀ n round
hfaithful₁ : faithful₁ n round
hcorrect₀ : correct₀ n round
hfa : trunc n a = a
hfb : trunc n b = b
hba : b ≤ a
no_uflow : a - b ≥ 2 ^ n
bpos : b > 0
le_two_mul : 2 * b ≥ a
⊢ trunc n (a - b) = a - b