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