Definition bool_fun_restrict (bf : bool_fun) (x : BDDvar)
(b : bool) (vb : var_binding) := bool_fun_eval bf (augment vb x b).

Lemma bool_fun_restrict_zero :
forall (x : BDDvar) (b : bool),
bool_fun_eq (bool_fun_restrict bool_fun_zero x b) bool_fun_zero.