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