proposition: Lemma gactV : {in D, forall a, {in R, {morph to^~ a : x / x^-1}}}.
proof: Proof. by move=> a Da /= x Rx; move; rewrite -!actmE ?morphV. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient)