proposition: Lemma quotient_subcent A B : 'C_A(B) / H \subset 'C_(A / H)(B / H).
proof: Proof. exact: morphim_subcent. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq div) mathcomp(choice fintype prime finset fingroup morphism) mathcomp(automorphism)