proposition: Theorem canwordP s : 's_[canword s] = s.
proof: Proof. Proof using. rewrite /= {2}(cocodeE s). rewrite -(big_map nat_of_ord xpredT) /=; apply congr_big => //. by rewrite canwordE. Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(fingroup perm morphism presentation) mathcomp(ssralg poly ssrint) permcomp tools permuted combclass congr