Definition is_tauto (be : bool_expr) :=
  Neqb BDDone (snd (BDDof_bool_expr initBDDconfig nil be)).

(* Specifications: *)
Lemma is_tauto_lemma : forall be : bool_expr, is_tauto be = true <-> bool_fun_eq bool_fun_one (bool_fun_of_bool_expr be).