proposition: Lemma pHall_sub pi A B : pi.-Hall(A) B -> B \subset A.
proof: Proof. by case/andP. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(fintype bigop finset prime fingroup morphism) mathcomp(gfunctor automorphism quotient action gproduct) mathcomp(cyclic)