Definition bool_fun_independent (bf : bool_fun) (x : BDDvar) :=
  forall vb : var_binding,
  bool_fun_eval bf (augment vb x true) =
  bool_fun_eval bf (augment vb x false).

Lemma in_dom_is_internal : forall (cfg : BDDconfig) (node : ad), in_dom _ node (fst cfg) = true -> is_internal_node cfg node.