∀ {α : Type u_1} {r : Std.Rco α} [inst : LE α] [inst_1 : LT α] [inst_2 : Std.PRange.UpwardEnumerable α]
  [Std.PRange.LawfulUpwardEnumerableLE α] [Std.PRange.LawfulUpwardEnumerableLT α] [Std.Rxo.IsAlwaysFinite α]
  [Std.PRange.LawfulUpwardEnumerable α] {a b : α}, r.lower ≤ b → (a ∈ b<...r.upper) → a ∈ r