proposition: Lemma injm_pelt pi x : x \in D -> pi.-elt (f x) = pi.-elt x.
proof: Proof. by move=> Dx; rewrite /p_elt order_injm. 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)