fact: Definition braidC := fun s : seq 'I_n => match s with | [:: a; b] => if (a.+1 < b) || (b.+1 < a) then [:: [:: b; a]] else [::] | _ => [::] end.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(fingroup perm morphism presentation) mathcomp(ssralg poly ssrint) permcomp tools permuted combclass congr