proposition: Lemma pi_pgroup p pi A : p.-group A -> p \in pi -> pi.-group A.
proof: Proof. exact: pi_pnat. Qed.
imports: mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(fintype bigop finset prime fingroup morphism) mathcomp(gfunctor automorphism quotient action gproduct) mathcomp(cyclic)