proposition: Lemma centerP A x : reflect (x \in A /\ centralises x A) (x \in 'Z(A)).
proof: Proof. exact: subcentP. 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)