∀ {α : Type u} {β : α → Type v} (k : α) (v : β k) (r : Std.DTreeMap.Internal.Impl α β) (hr : r.Balanced)
  (hr_2 : Std.DTreeMap.Internal.Impl.leaf.Balanced),
  Std.DTreeMap.Internal.Impl.link k v Std.DTreeMap.Internal.Impl.leaf r hr_2 hr =
    { impl := (Std.DTreeMap.Internal.Impl.insertMin k v r ⋯).impl, balanced_impl := ⋯, size_impl := ⋯ }