proposition: Lemma astabsU : 'N(S | to) :&: 'N(T | to) \subset 'N(S :|: T | to).
proof: Proof. by rewrite -(astabsC S) -(astabsC T) -(astabsC (S :|: T)) setCU astabsI. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient)