proposition: Lemma postfixpoint_charact: IdentSet.Subset (F postfixpoint) postfixpoint \/ postfixpoint = default.
proof: Proof. unfold postfixpoint. generalize niter, IdentSet.empty. induction n; intros; cbn. - auto. - destruct (IdentSet.subset (F t) t) eqn:SUBSET. + left. apply IdentSet.subset_2; auto. + apply IHn. Qed.
imports: Coq(ZArith Psatz Bool String Program.Equality FSets Wellfounded) CDF(Sequences IMP Simulation)