proposition: Lemma isog_pcore pi : G \isog H -> 'O_pi(G) \isog 'O_pi(H).
proof: Proof. exact: gFisog. 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)