proposition: Lemma fproperIr A B : ~~ (B `<=` A) -> A `&` B `<` B.
proof: Proof. by move=> nsAB; rewrite fproperE fsubsetIr fsubsetI negb_and nsAB. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)