proposition: Lemma app_nil_r : forall l, l ++ nil = l.
proof: Proof. Proof using. induction l. auto. rewrite app_cons_l. fequals~. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation)