proposition: Lemma injm_dprodm : 'injm dprodm = [&& 'injm fH, 'injm fK & fH @* H :&: fK @* K == 1].
proof: Proof. rewrite injm_cprodm -(morphimIdom fH K). by case/dprodP: eqHK_G => _ _ _ ->; rewrite morphim1. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(quotient action)