(*s Adding a lis of adresses connected to [root] with weight $0$ *)
Fixpoint CG_add_root (root : ad) (cg : CGraph1) (l : list ad) {struct l} :
CGraph1 :=
match l with
| nil => cg
| x :: l' => CG_add_root root (CG_add cg root x Dz) l'
end.

Lemma CG_add_root_rooted_3 :
forall (cg : CGraph1) (root : ad),
in_dom _ root cg = false ->
forall a : ad,
in_dom _ a cg = true ->
CG_edge (CG_add_root root cg (ad_list_of_dom _ cg)) root a = Some Dz.