(** (Note the use of [app_nil_r] to change the goal of the theorem to exactly the same shape expected by [MStarApp].) *)
(** **** Exercise: 3 stars (exp_match_ex1)  *)
(** The following lemmas show that the informal matching rules given at the beginning of the chapter can be obtained from the formal inductive definition. *)

Lemma empty_is_empty : forall T (s : list T),
~ (s =~ EmptySet).