proposition: Lemma Nth_app_r' : forall n m x l1 l2, Nth m l2 x -> n = (m + length l1)%nat -> Nth n (l1 ++ l2) x.
proof: Proof. Proof using. intros. subst. applys* Nth_app_r. Qed.
imports: Coq.Classes.Morphisms TLC(LibTactics LibLogic LibReflect LibOperation LibProd LibOption LibNat LibInt LibWf LibMonoid LibRelation)