proposition: Lemma tuto_setIA : forall A B C, A :&: (B :&: C) = A :&: B :&: C.
proof: Proof. by move=> A B C; apply/setP=> x; rewrite !inE andbA. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq path) mathcomp(choice fintype tuple finset)