Goal:
    A : Type  l : list A  x : A
  ============================
   (#|l| = #|l| + 1 - 1)


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