proposition: Lemma lift_1: forall f n1 n2 N1 N2, In n1 N1 -> In n2 N2 -> In (f n1 n2) (lift f N1 N2).
proof: Proof. unfold In, lift; intros. destruct N1, N2; try tauto. congruence. Qed.
imports: Coq(ZArith Psatz Bool String List FMaps) CDF(Sequences IMP)