proposition: Lemma im_sdprodm : sdprodm @* G = fH @* H * fK @* K.
proof: Proof. by rewrite -morphim_sdprodm //; case/sdprodP: eqHK_G => _ ->. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(quotient action)