∀ {α : Type u} {r : Std.Roo α} [inst : LT α] [inst_1 : DecidableLT α] [inst_2 : Std.PRange.UpwardEnumerable α]
  [inst_3 : Std.PRange.LawfulUpwardEnumerable α] [Std.PRange.LawfulUpwardEnumerableLT α]
  [inst_5 : Std.Rxo.IsAlwaysFinite α] {i : ℕ},
  i < r.toList.length → (Std.PRange.succMany? (i + 1) r.lower).isSome = true