(** ** Properties of [Z_one_bits] and [is_power2]. *)
Fixpoint powerserie (l: list Z): Z :=
match l with
| nil => 0
| x :: xs => two_p x + powerserie xs
end.

Lemma Z_one_bits_powerserie:
forall x, 0 <= x < modulus -> x = powerserie (Z_one_bits wordsize x 0).