proposition: Lemma coprimeSg G H p : H \subset G -> coprime #|G| p -> coprime #|H| p.
proof: Proof. by move=> sHG; apply: coprime_dvdl (cardSg sHG). Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)