proposition: Lemma fsetKIid A B : A `&` (A `&` B) = A `&` B.
proof: Proof. by rewrite fsetIA fsetIid. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)