Definition BDDor :=
  BDDor_1 gc cfg ul node1 node2
    (S
       (max (nat_of_N (node_height cfg node1))
          (nat_of_N (node_height cfg node2)))).

Lemma BDDor_list_OK_cons : used_list_OK (fst BDDor) (snd BDDor :: ul).