∀ {α : Type u} [inst : Std.PRange.UpwardEnumerable α] [inst_1 : Std.PRange.Least? α]
  [Std.PRange.LawfulUpwardEnumerable α] [Std.PRange.LawfulUpwardEnumerableLeast? α] {r : Std.Rii α} {a : α},
  (Std.Rii.Internal.iter r).IsPlausibleIndirectOutput a ↔ a ∈ r