proposition: Lemma bigfcup_undup P F : \bigcup_(i <- undup r | P i) F i = \bigcup_(i <- r | P i) F i.
proof: Proof. by rewrite big_undup => //= A; rewrite fsetUid. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)