proposition: Lemma psubgroupJ pi G H x : x \in G -> pi.-subgroup(G) (H :^ x) = pi.-subgroup(G) H.
proof: Proof. by move=> Gx; rewrite /psubgroup pgroupJ -{1}(conjGid Gx) conjSg. 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)