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