Section Facts.
Variable A : Type.
(** *** Generic facts *)
(** Destruction *)
(** *** Head and tail *)
(************************)
(** *** Facts about [In] *)
(************************)
(** Characterization of [In] *)
Hint Resolve app_assoc_reverse : core.
(* end hide *)
(** Facts deduced from the result of a concatenation *)

Theorem app_eq_unit :
forall (x y:list A) (a:A),
x ++ y = [a] -> x = [] /\ y = [a] \/ x = [a] /\ y = [].