proposition: Lemma fsetIUr A B C : A `&` (B `|` C) = (A `&` B) `|` (A `&` C).
proof: Proof. by apply/fsetP=> x; rewrite !inE andb_orr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)