∀ {α : Type u} {β : α → Type v} {cmp : α → α → Ordering} {t : Std.DTreeMap.Raw α β cmp} [Std.TransCmp cmp],
  t.WF →
    ∀ {k fallback : α},
      (t.erase k).isEmpty = false →
        ¬cmp k (t.minKeyD fallback) = Ordering.eq → (t.erase k).minKeyD fallback = t.minKeyD fallback