(** * Addendum to the standard library of Coq *)
Require Export Omega.
Global Obligation Tactic := idtac.
Notation "[ x ; .. ; y ]" := (cons x .. (cons y nil) .. ).

Lemma tl_app : forall A (l1 l2 : list A),
l1 <> nil ->
tl (l1 ++ l2) = tl l1 ++ l2.