proposition: Lemma centsP A B : reflect {in A, centralised B} (A \subset 'C(B)).
proof: Proof. by apply: (iffP subsetP) => cAB x /cAB/centP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)