calc ulp n (b - w - a - ulp n (b - w - 1))
  _ ∣ ulp n (b - w - a) := ulp_dvd_ulp n tsub_le_self
  _ ∣ b - w - a         := ulp_dvd_of_trunc_eq $ hfb₁ ▸ ih
case succ.inl.h₁
n a b : ℕ
npos : 0 < n
hfb : trunc n b = b
hf : trunc n (b - a) = b - a
w : ℕ
h : 2 * a < b - Nat.succ w
ih : trunc n (trunc n (b - w) - a) = trunc n (b - w) - a
hfb₁ : trunc n (b - w) = b - w
bpos : 0 < b - w
⊢ ulp n (b - w - a - ulp n (b - w - 1)) ∣ b - w - a
no goals