Canonical xcprod_morphism := [morphism of xcprodm].

(* Uses gzZchar. *)
Lemma Aut_cprod_by_full :
Aut_in (Aut H) 'Z(H) \isog Aut 'Z(H) ->
Aut_in (Aut K) 'Z(K) \isog Aut 'Z(K) ->
Aut_in (Aut C) 'Z(C) \isog Aut 'Z(C).