CoFixpoint memo_make (n:nat) : Stream A := Cons (f n) (memo_make (S n)).Definition memo_list := memo_make 0.Fixpoint memo_get (n:nat) (l:Stream A) : A :=
  match n with
    | O => hd l
    | S n1 => memo_get n1 (tl l)
  end.

Theorem memo_get_correct: forall n, memo_get n memo_list = f n.