Definition BDDvar_make (cfg : BDDconfig) (x : BDDvar) :=
  BDDmake cfg x BDDzero BDDone.

Lemma BDDvar_make_keeps_node_OK : forall (cfg : BDDconfig) (x : BDDvar), BDDconfig_OK cfg -> forall node : ad, config_node_OK cfg node -> config_node_OK (fst (BDDvar_make cfg x)) node.