rewrite [next, ulp_trunc npos]
case hdvd.h₁
round : ℕ → ℕ
n a b : ℕ
npos : 0 < n
hfaithful₁ : faithful₁ n round
hfa : trunc n a = a
hfb : trunc n b = b
hba : b ≤ a
lt_round : a + b < round (a + b)
ulp_sub_le : ulp n (a + b) - (a + b) % ulp n (a + b) ≤ b
⊢ ulp n b ∣ next n (trunc n (a + b))
case hdvd.h₁
round : ℕ → ℕ
n a b : ℕ
npos : 0 < n
hfaithful₁ : faithful₁ n round
hfa : trunc n a = a
hfb : trunc n b = b
hba : b ≤ a
lt_round : a + b < round (a + b)
ulp_sub_le : ulp n (a + b) - (a + b) % ulp n (a + b) ≤ b
⊢ ulp n b ∣ trunc n (a + b) + ulp n (a + b)