proposition: Lemma ract_is_action : is_action A (ract sAD).
proof: Proof. rewrite /ract; case: to => f [injf fM]. by split=> // x; apply: (sub_in2 (subsetP sAD)). Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient)