proposition: Lemma odd_pgroup_odd p G : odd p -> p.-group G -> odd #|G|.
proof: Proof. move=> p_odd pG; rewrite odd_2'nat (pi_pnat pG) // !inE. by case: eqP p_odd => // ->. 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)