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

Lemma app_length : forall l l' : list A, length (l++l') = length l + length l'.