proposition: Lemma braidred_catl (u v w : seq 'I_n) : braid_reduces u v -> braid_reduces (u ++ w) (v ++ w).
proof: Proof. Proof using. rewrite /braid_reduces => /orP[/braid_catl -> // |] /reduces_catl ->. by rewrite orbT. Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(fingroup perm morphism presentation) mathcomp(ssralg poly ssrint) permcomp tools permuted combclass congr