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