proposition: Lemma injm_cprodm : 'injm cprodm = [&& 'injm fH, 'injm fK & fH @* H :&: fK @* K == fH @* K].
proof: Proof. by rewrite ker_cprodm -(ker_pprodm cprodm_norm cprodm_actf eqfHK) injm_pprodm. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(quotient action)