proposition: Lemma gact_out x a : a \in D -> x \notin R -> to x a = x.
proof: Proof. by move=> Da Rx; rewrite -actpermE (out_Aut _ Rx) ?actperm_Aut. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient)