Section Dprodm.
Variables G H K : {group gT}.
Variables (fH : {morphism H >-> rT}) (fK : {morphism K >-> rT}).
Hypothesis eqHK_G : H \x K = G.
Hypothesis cfHK : fK @* K \subset 'C(fH @* H).
End Dprodm.

Lemma isog_dprod A B G C D L :
A \x B = G -> C \x D = L -> isog A C -> isog B D -> isog G L.