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