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