Notation memo_val := (memo_val A).(** For a dependent function, the previous solution is
    reused thanks to a temporary hiding of the dependency
    in a "container" [memo_val]. *)

#[universes(template)]
Inductive memo_val {A : nat -> Type} : Type :=
  memo_mval: forall n, A n -> memo_val.Fixpoint is_eq (n m : nat) : {n = m} + {True} :=
  match n, m return {n = m} + {True} with
  | 0, 0 =>left True (eq_refl 0)
  | 0, S m1 => right (0 = S m1) I
  | S n1, 0 => right (S n1 = 0) I
  | S n1, S m1 =>
     match is_eq n1 m1 with
     | left H => left True (f_equal S H)
     | right _ => right (S n1 = S m1) I
     end
  end.Definition memo_get_val n (v: memo_val): A n :=
match v with
| memo_mval m x =>
    match is_eq n m with
    | left H =>
       match H in (eq _ y) return (A y -> A n) with
        | eq_refl => fun v1 : A n => v1
       end
    | right _ => fun _ : A m => f n
    end x
end.Definition dmemo_list := memo_list _ mf.Definition dmemo_get n l := memo_get_val n (memo_get _ n l).

Theorem dmemo_get_correct: forall n, dmemo_get n dmemo_list = f n.