. apply Nat.add_le_add_left
  exact lt_round.le
round : ℕ → ℕ
n a b : ℕ
npos : 0 < n
hfaithful₀ : faithful₀ n round
hfaithful₁ : faithful₁ n round
hfa : trunc n a = a
hba : 2 * b ≤ a
lt_round : a - b < round (a - b)
hba' : b ≤ a
⊢ b + (a - b) ≤ b + round (a - b)
no goals