(*s Properties of the range of the graph *)

Definition cg_range := DMerge D.

Lemma cg_range_4 : forall (cg : CGraph1) (x y : ad) (d : D) (a : ad), in_dom D a (cg_range (CG_add cg x y d)) = Neqb a y || in_dom D a (cg_range cg).