rewrite [tsub_right_comm]
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
round_le : round (a - b) ≤ a - b
no_uflow : a - b ≥ 2 ^ n
ulp_le' : ulp n (a - b) ≤ 2 * b
hca : round (a - b) ≤ a
ulp_even : 2 ∣ ulp n (a - b)
hfd : trunc n (a - round (a - b) - b) = a - round (a - b) - b
⊢ round (a - b) + (a - round (a - b) - b) = a - b
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
round_le : round (a - b) ≤ a - b
no_uflow : a - b ≥ 2 ^ n
ulp_le' : ulp n (a - b) ≤ 2 * b
hca : round (a - b) ≤ a
ulp_even : 2 ∣ ulp n (a - b)
hfd : trunc n (a - round (a - b) - b) = a - round (a - b) - b
⊢ round (a - b) + (a - b - round (a - b)) = a - b