proposition: Corollary braid_reduced (v w : seq 'I_n) : v =Br w -> v \is reduced -> w \is reduced.
proof: Proof. Proof using. rewrite unfold_in => Hbr. by rewrite (braid_prods Hbr) (size_braid Hbr). Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(fingroup perm morphism presentation) mathcomp(ssralg poly ssrint) permcomp tools permuted combclass congr