∀ {α : Type u} {β : α → Type v} {cmp : α → α → Ordering} {t : Std.DTreeMap.Raw α β cmp} [inst : BEq α]
  [Std.TransCmp cmp] [Std.LawfulBEqCmp cmp],
  t.WF →
    ∀ {k : α} {v : β k},
      (t.insert k v).toList.Perm (⟨k, v⟩ :: List.filter (fun x => decide ¬(k == x.fst) = true) t.toList)