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