simpl; auto.
Qed.
Fixpoint iter {A: Type} (f: A -> A) (n: nat) (x: A) :=
match n with
| O => x
| S n1 => f (iter f n1 x)
end.
(* A bit of ssreflect *)
Coercion b2Prop (x : bool) := x = true.

(* Some facts about div2 *)
Lemma div2_double_p n m : div2 (2 * n + m) = n + div2 m.