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