∀ {α : Type u} {β : Type v} [inst : Inhabited (α × β)] (size : ℕ) (k : α) (v : β)
  (r : Std.DTreeMap.Internal.Impl α fun x => β),
  Std.DTreeMap.Internal.Impl.Const.minEntry!
      (Std.DTreeMap.Internal.Impl.inner size k v Std.DTreeMap.Internal.Impl.leaf r) =
    (k, v)