proposition: Lemma ract_is_groupAction : is_groupAction R (to \ sAD).
proof: Proof. by move=> a Aa /=; rewrite ractpermE actperm_Aut ?(subsetP sAD). Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient)