proposition: Lemma setUidPl A B : reflect (A :|: B = A) (B \subset A).
proof: Proof. by rewrite -setCS (sameP setIidPl eqP) -setCU (inj_eq setC_inj); apply: eqP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop)