proposition: Lemma fsetUidPl A B : reflect (A `|` B = A) (B `<=` A).
proof: Proof. by rewrite fsetUC; apply/fsetUidPr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)