∀ {α : Type u} {β : α → Type v} [inst : Inhabited ((a : α) × β a)] (size : ℕ) (k : α) (v : β k)
  (r : Std.DTreeMap.Internal.Impl α β),
  (Std.DTreeMap.Internal.Impl.inner size k v Std.DTreeMap.Internal.Impl.leaf r).minEntry! = ⟨k, v⟩