proposition: Lemma prefix_snoc_length: forall ys y xs, prefix (ys & y) xs -> length ys < length xs.
proof: Proof. Proof using. intros ys y xs [ zs ? ]. subst xs. rew_list. math. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation LibList)