proposition: Lemma centerC A : {in A, centralised 'Z(A)}.
proof: Proof. by apply/centsP; rewrite centsC subsetIr. 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)