(* semantics for mu_calculus formulae; but the fixpoint operator is instead
   interpreted as iteration of a function atmost 2^n times *)
Fixpoint mu_eval (f : mu_form) : rel_env -> bool_expr :=
  fun re =>
  match f with
  | mu_0 => Zero
  | mu_1 => One
  | mu_ap p => Var p
  | mu_rel_var P => re P
  | mu_neg g => Neg (mu_eval g re)
  | mu_and g h => ANd (mu_eval g re) (mu_eval h re)
  | mu_or g h => Or (mu_eval g re) (mu_eval h re)
  | mu_impl g h => Impl (mu_eval g re) (mu_eval h re)
  | mu_iff g h => Iff (mu_eval g re) (mu_eval h re)
  | mu_all t g => mu_all_eval N (te t) (mu_eval g re)
  | mu_ex t g => mu_ex_eval N (te t) (mu_eval g re)
  | mu_mu P g =>
      fst (iter2n _ be_eq_dec (fun be => mu_eval g (re_put re P be)) Zero N)
  end.Definition re_to_be_inc (f : rel_env -> bool_expr) 
  (P : ad) :=
  forall (re : rel_env) (be1 be2 : bool_expr),
  be_le be1 be2 -> be_le (f (re_put re P be1)) (f (re_put re P be2)).Definition re_to_be_dec (f : rel_env -> bool_expr) 
  (P : ad) :=
  forall (re : rel_env) (be1 be2 : bool_expr),
  be_le be1 be2 -> be_le (f (re_put re P be2)) (f (re_put re P be1)).Definition ad_to_be_ok (vf : ad -> bool) (abe : ad -> bool_expr) :=
  forall x : ad, be_ok vf (abe x).Definition ad_to_be_eq (f1 f2 : ad -> bool_expr) :=
  forall x : ad, be_eq (f1 x) (f2 x).

Lemma mu_ex_eval_lu : forall t be : bool_expr, be_ok (var_lu 0 (2 * N)) t -> be_ok (var_lu 0 N) be -> be_ok (var_lu 0 N) (mu_ex_eval N t be).