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 bool_fun_neq_zero_one :
forall cfg : BDDconfig,
BDDconfig_OK cfg ->
~ bool_fun_eq (bool_fun_of_BDD cfg BDDzero) (bool_fun_of_BDD cfg BDDone).