proposition: Lemma setU_eq0 A B : (A :|: B == set0) = (A == set0) && (B == set0).
proof: Proof. by rewrite -!subset0 subUset. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop)