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 *)

Lemma app_inj_tail :
forall (x y:list A) (a b:A), x ++ [a] = y ++ [b] -> x = y /\ a = b.