proposition: Lemma actsQ A B H : A \subset 'N(H) -> A \subset 'N(B) -> [acts A, on B / H | 'Q].
proof: Proof. by move=> nHA nBA; rewrite acts_quotient // subsetI dom_qactJ nHA astabsJ. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient)