proposition: Lemma plength1_Sylow_sub_der1 : S \subset G^`(1) -> S \subset ('N_G(S))^`(1).
proof: Proof. by move/setIidPl=> sSG'; apply/setIidPl; rewrite -(pprod_focal_coprime defG). Qed.
imports: mathcomp.ssreflect.ssreflect mathcomp(ssrfun ssrbool eqtype ssrnat seq div fintype finset) mathcomp(prime fingroup morphism automorphism quotient gproduct gfunctor) mathcomp(cyclic center commutator pgroup nilpotent sylow abelian hall) mathcomp(maximal) odd_order(BGsection1 BGappendixAB)