Section Isomorphism.
Let gzZ_lone (Y : {group gTK}) :
Y \subset 'Z(K) -> gz @* 'Z(H) \isog Y -> gz @* 'Z(H) = Y.
Variables (rT : finGroupType) (GH GK G : {group rT}).
Hypotheses (defG : GH \* GK = G) (ziGHK : GH :&: GK = 'Z(GH)).
Hypothesis AutZHfull : Aut_in (Aut H) 'Z(H) \isog Aut 'Z(H).
Hypotheses (isoGH : GH \isog H) (isoGK : GK \isog K).
Definition xcprod := cprod_by (svalP xcprod_subproof).
Inductive xcprod_spec : finGroupType -> Prop :=
XcprodSpec gz isoZ : xcprod_spec (@cprod_by gTH gTK H K gz isoZ).

Lemma xcprodP : 'Z(H) \isog 'Z(K) -> xcprod_spec xcprod.