proposition: Lemma canonical_uniq ks : canonical_keys ks -> uniq ks.
proof: Proof. by move=> /eqP <-; exact: sort_keys_uniq. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop)