proposition: Lemma app_not_empty_l : forall l1 l2, l1 <> nil -> l1 ++ l2 <> nil.
proof: Proof. Proof using. introv NE K. apply NE. forwards*: app_eq_nil_inv K. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation)