∀ {α : Type u} {β : α → Type v} {instOrd : Ord α} {t : Std.DTreeMap.Internal.Impl α β} [Std.TransOrd α] (h : t.WF)
  {k fallback : α},
  (Std.DTreeMap.Internal.Impl.erase k t ⋯).impl.isEmpty = false →
    ¬compare k (t.minKeyD fallback) = Ordering.eq →
      (Std.DTreeMap.Internal.Impl.erase k t ⋯).impl.minKeyD fallback = t.minKeyD fallback