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diff --git a/theories/ZArith/Zpow_def.v b/theories/ZArith/Zpow_def.v
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+++ b/theories/ZArith/Zpow_def.v
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+Require Import ZArith_base.
+Require Import Ring_theory.
+
+Open Local Scope Z_scope.
+ 
+(** [Zpower_pos z n] is the n-th power of [z] when [n] is an binary
+      integer (type [positive]) and [z] a signed integer (type [Z]) *) 
+Definition Zpower_pos (z:Z) (n:positive) := iter_pos n Z (fun x:Z => z * x) 1.
+  
+Definition Zpower (x y:Z) :=
+    match y with
+      | Zpos p => Zpower_pos x p
+      | Z0 => 1
+      | Zneg p => 0
+    end.
+
+Lemma Zpower_theory : power_theory 1 Zmult (eq (A:=Z)) Z_of_N Zpower.
+Proof.
+ constructor. intros.
+ destruct n;simpl;trivial.
+ unfold Zpower_pos.
+ assert (forall k, iter_pos p Z (fun x : Z => r * x) k = pow_pos Zmult r p*k).
+ induction p;simpl;intros;repeat rewrite IHp;trivial;
+   repeat rewrite Zmult_assoc;trivial.
+ rewrite H;rewrite Zmult_1_r;trivial.
+Qed.
+