. exact tsub_le_self
case hle
n x : ℕ
npos : 0 < n
⊢ trunc n x - ulp n x ≤ ?x

case hdvd
n x : ℕ
npos : 0 < n
⊢ ulp n ?x ∣ trunc n x - ulp n x

case x
n x : ℕ
npos : 0 < n
⊢ ℕ
case hdvd
n x : ℕ
npos : 0 < n
⊢ ulp n (trunc n x) ∣ trunc n x - ulp n x