proposition: Lemma pcore_sub G : 'O_pi(G) \subset G.
proof: Proof. by case/andP: (pcore_psubgroup G). 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)