diff -r 5c74f003a68e -r 0187f936685a src/HOL/RelPow.thy
--- a/src/HOL/RelPow.thy	Fri Oct 30 10:43:12 1998 +0100
+++ b/src/HOL/RelPow.thy	Fri Oct 30 10:45:08 1998 +0100
@@ -8,6 +8,9 @@
 
 RelPow = Nat +
 
+instance
+  set :: (term) {power}   (* only ('a * 'a) set should be in power! *)
+
 primrec
   "R^0 = Id"
   "R^(Suc n) = R O (R^n)"