∀ {α : Type u} {β : α → Type v} {cmp : α → α → Ordering} {t : Std.DTreeMap.Raw α β cmp} [Std.TransCmp cmp]
  [inst : Std.LawfulEqCmp cmp],
  t.WF → ∀ {a : α} [inst_1 : Inhabited (β a)], t.contains a = true → t.get? a = some (t.get! a)