proposition: Lemma inj_leq m n (f : 'I_m -> 'I_n) : injective f -> m <= n.
proof: Proof. by move=> /leq_card; rewrite !card_ord. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(path div)