. trans ulp n a
  . exact ulp_dvd_ulp n hba
  . exact ulp_dvd_of_trunc_eq hfa
case hdvd.h₁
n a b : ℕ
hfa : trunc n a = a
hfb : trunc n b = b
hba : b ≤ a
hab : a ≤ b + b
⊢ ulp n b ∣ a

case hdvd.h₂
n a b : ℕ
hfa : trunc n a = a
hfb : trunc n b = b
hba : b ≤ a
hab : a ≤ b + b
⊢ ulp n b ∣ b
case hdvd.h₂
n a b : ℕ
hfa : trunc n a = a
hfb : trunc n b = b
hba : b ≤ a
hab : a ≤ b + b
⊢ ulp n b ∣ b