proposition: Lemma morph_p_elt pi x : x \in D -> pi.-elt x -> pi.-elt (f x).
proof: Proof. by move=> Dx; apply: pnat_dvd; apply: morph_order. 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)