proposition: Lemma sub_abelian_cent2 : B \subset A -> C \subset A -> B \subset 'C(C).
proof: Proof. by move=> sBA; move/sub_abelian_cent; apply: subset_trans. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)