some jokes are just too bad to appear in a theory file

--- a/src/HOL/Nat.thy	Fri Apr 24 18:01:39 2009 +0200
+++ b/src/HOL/Nat.thy	Fri Apr 24 18:20:37 2009 +0200
@@ -1206,7 +1206,7 @@
   "funpow (Suc n) f = f o funpow n f"
   unfolding funpow_code_def by simp_all
 
-definition "foo = id ^^ (1 + 1)"
+hide (open) const funpow
 
 lemma funpow_add:
   "f ^^ (m + n) = f ^^ m \<circ> f ^^ n"