proposition: Lemma reducedP w : reflect (length 's_[w] = size w) (w \is reduced).
proof: Proof. by rewrite unfold_in; apply/eqP. Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(fingroup perm morphism presentation) mathcomp(ssralg poly ssrint) permcomp tools permuted combclass congr