exact round_sub_le npos hfaithful₀ hfaithful₁ b hfa
case inl.hba
round : ℕ → ℕ
n a b : ℕ
npos : 0 < n
hfaithful₀ : faithful₀ n round
hfaithful₁ : faithful₁ n round
hfa : trunc n a = a
hfb : trunc n b = b
hba : b ≤ a
hab' : 2 * b ≤ a
⊢ round (a - b) ≤ a
no goals