proposition: Lemma fsetIC (A B : {fset K}) : A `&` B = B `&` A.
proof: Proof. by apply/fsetP => a; rewrite !inE andbC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)