proposition: Lemma normsR : A \subset 'N([~: B, C]).
proof: Proof. by apply/normsP=> x Ax; rewrite conjsRg !(normsP _ x Ax). Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)