Inductive Const_leq (s : nat) : term -> Prop :=
| IdLe : forall x, Const_leq s (Id x)
| ConstLe : forall n, n <= s -> Const_leq s (Const n)
| AppLe :
    forall t1 t2, 
      Const_leq s t1 -> Const_leq s t2 ->
      Const_leq s (App t1 t2)
| AbsLe :
    forall t,
      Const_leq s t -> Const_leq s (Abs t).Inductive Const_leq (s : nat) : term -> Prop :=
| IdLe : forall x, Const_leq s (Id x)
| ConstLe : forall n, n <= s -> Const_leq s (Const n)
| AppLe :
    forall t1 t2, 
      Const_leq s t1 -> Const_leq s t2 ->
      Const_leq s (App t1 t2)
| AbsLe :
    forall t,
      Const_leq s t -> Const_leq s (Abs t).Inductive Const_leq (s : nat) : term -> Prop :=
| IdLe : forall x, Const_leq s (Id x)
| ConstLe : forall n, n <= s -> Const_leq s (Const n)
| AppLe :
    forall t1 t2, 
      Const_leq s t1 -> Const_leq s t2 ->
      Const_leq s (App t1 t2)
| AbsLe :
    forall t,
      Const_leq s t -> Const_leq s (Abs t).Inductive Const_leq (s : nat) : term -> Prop :=
| IdLe : forall x, Const_leq s (Id x)
| ConstLe : forall n, n <= s -> Const_leq s (Const n)
| AppLe :
    forall t1 t2, 
      Const_leq s t1 -> Const_leq s t2 ->
      Const_leq s (App t1 t2)
| AbsLe :
    forall t,
      Const_leq s t -> Const_leq s (Abs t).Inductive Const_leq (s : nat) : term -> Prop :=
| IdLe : forall x, Const_leq s (Id x)
| ConstLe : forall n, n <= s -> Const_leq s (Const n)
| AppLe :
    forall t1 t2, 
      Const_leq s t1 -> Const_leq s t2 ->
      Const_leq s (App t1 t2)
| AbsLe :
    forall t,
      Const_leq s t -> Const_leq s (Abs t).Fixpoint max_const (t : term) : nat :=
  match t with 
    | Id _ => 0
    | Const n => n
    | App t1 t2 => max (max_const t1) (max_const t2)
    | Abs t => max_const t
  end.

Lemma max_const_Const_leq : forall t, Const_leq (max_const t) t.