have l : round (a + b) = a + b := round_eq_of_trunc_eq npos hfaithful₀ k
round : ℕ → ℕ
n a b : ℕ
npos : 0 < n
hfaithful₀ : faithful₀ n round
uflow : a + b < 2 ^ n
k : trunc n (a + b) = a + b
⊢ trunc n (a + b - round (a + b)) = a + b - round (a + b) ∧ trunc n (round (a + b) - (a + b)) = round (a + b) - (a + b)
round : ℕ → ℕ
n a b : ℕ
npos : 0 < n
hfaithful₀ : faithful₀ n round
uflow : a + b < 2 ^ n
k : trunc n (a + b) = a + b
l : round (a + b) = a + b
⊢ trunc n (a + b - round (a + b)) = a + b - round (a + b) ∧ trunc n (round (a + b) - (a + b)) = round (a + b) - (a + b)