proposition: Lemma iter_sub_ffix k : iterF k `<=` fixfset.
proof: Proof. by rewrite /fixfset !fset_iterFE; apply/subset_imfset/subsetP/iter_sub_fix. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)