Goal:
  
  A : Type
  f : nat → A
  n : nat
  t : A
  Hn : nth_error (unfold 0 f) n = Some t
  ============================
   (t = f n)


DEBUG:Going to execute:
intros; Zify.zify_pre_hook; zify_elim_let; zify_op;
            Zify.zify_iter_specs