Inductive list : nat -> Set :=
    | nil : list 0
    | cons : forall n : nat, A -> list n -> list (S n).Inductive list : nat -> Set :=
    | nil : list 0
    | cons : forall n : nat, A -> list n -> list (S n).Inductive list : nat -> Set :=
    | nil : list 0
    | cons : forall n : nat, A -> list n -> list (S n).Definition eq_list := eq_dep nat list.Definition hd (n : nat) (l : list n) : Exc A :=
    match l in (list m) return (Exc A) with
    | nil => error
    | cons p a l' => value a
    end.Definition head (n : nat) (l : list n) :=
    match l in (list p) return (0 < p -> A) with
    | nil =>
        (* nil*)	
        fun h : 0 < 0 => False_rec A (lt_irrefl 0 h)
        (*cons p a l' *)
    | cons p a l' => fun h : 0 < S p => a
    end.Definition Head (n : nat) (l : list (S n)) := head (S n) l (lt_O_Sn n).Definition tl (n : nat) (l : list n) : list (pred n) :=
    match l in (list m) return (list (pred m)) with
    | nil => nil
    | cons p a l' => l'
    end.

Lemma empty : forall l : list 0, nil = l.