∀ {α : Type u} [inst : Std.PRange.UpwardEnumerable α] [Std.PRange.LawfulUpwardEnumerable α]
  [inst_2 : Std.PRange.InfinitelyUpwardEnumerable α] {a b : α},
  Std.PRange.UpwardEnumerable.LT (Std.PRange.succ a) b →
    ∃ b', b = Std.PRange.succ b' ∧ Std.PRange.UpwardEnumerable.LT a b'