∀ {α : Type u} {β : α → Type v} {cmp : α → α → Ordering} {t : Std.ExtDTreeMap α β cmp} [inst : Std.TransCmp cmp]
  {k km kme : α} (hkme : (t.erase k).maxKey? = some kme), t.maxKey?.get ⋯ = km → (cmp kme km).isLE = true