have h2 : trunc n x ≤ x := trunc_le n x
case inr
n x : ℕ
round : ℕ → ℕ
npos : 0 < n
hcorrect₀ : correct₀ n round
hlo : round x = trunc n x
no_uflow : x ≥ 2 ^ n
h1 : x ≤ next n (trunc n x)
⊢ 2 * x ≤ trunc n x + next n (trunc n x)
case inr
n x : ℕ
round : ℕ → ℕ
npos : 0 < n
hcorrect₀ : correct₀ n round
hlo : round x = trunc n x
no_uflow : x ≥ 2 ^ n
h1 : x ≤ next n (trunc n x)
h2 : trunc n x ≤ x
⊢ 2 * x ≤ trunc n x + next n (trunc n x)