proposition: Lemma mulGidPr G H : reflect (G * H = H) (G \subset H).
proof: Proof. by apply: (iffP idP) => [|<-]; [apply: mulSGid | apply: mulG_subl]. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)