proposition: Lemma ncprod0 : G_ 0 \isog 'Z(G).
proof: Proof. by rewrite [ncprod]unlock isog_sym isog_subg. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(fintype bigop finset fingroup morphism perm) mathcomp(automorphism quotient action gproduct gfunctor) mathcomp(cyclic)