∀ {α : Type u} {r : Std.Roi α} [inst : Std.PRange.UpwardEnumerable α] [inst_1 : Std.Rxi.HasSize α]
  [Std.PRange.LawfulUpwardEnumerable α] [Std.Rxi.IsAlwaysFinite α] [Std.Rxi.LawfulHasSize α],
  r.size =
    match Std.PRange.succ? r.lower with
    | none => 0
    | some next => next<...*.size + 1