proposition: Lemma pHallNK pi G H : pi^'^'.-Hall(G) H = pi.-Hall(G) H.
proof: Proof. exact: eq_pHall (negnK _). 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)