proposition: Lemma normalP A B : reflect (A \subset B /\ {in B, normalised A}) (A <| B).
proof: Proof. by apply: (iffP andP)=> [] [sAB]; move/normsP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)