proposition: Lemma p'groupEpi p G : p^'.-group G = (p \notin \pi(G)).
proof: Proof. exact: p'natEpi (cardG_gt0 G). 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)