proposition: Lemma reduceK s : reduced s -> perm_eq (reduce s) s.
proof: Proof. by move/reduce_reduced=> ->; rewrite perm_rev. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order generic_quotient) mathcomp(ssralg ssrnum ssrint)