proposition: Lemma ncprodS n : xcprod_spec G [set: ncprod n] (ncprod n.+1).
proof: Proof. by have:= xcprodP (isog_symr (center_ncprod n)); rewrite [ncprod]unlock. 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)