proposition: Lemma prodsV w : 's_[rev w] = 's_[w]^-1.
proof: Proof. Proof using. by apply/eqP; rewrite eq_sym eq_invg_mul prodsK. Qed.
imports: HB(structures) mathcomp(all_ssreflect) mathcomp(fingroup perm morphism presentation) mathcomp(ssralg poly ssrint) permcomp tools permuted combclass congr