diff -r 28f5ed40ecab -r 89c37daebfdd src/HOL/Library/List_Set.thy
--- a/src/HOL/Library/List_Set.thy	Sat Jun 27 22:28:07 2009 +0200
+++ b/src/HOL/Library/List_Set.thy	Sun Jun 28 10:33:36 2009 +0200
@@ -70,7 +70,7 @@
   by (auto simp add: remove_def remove_all_def)
 
 lemma image_set:
-  "image f (set xs) = set (remdups (map f xs))"
+  "image f (set xs) = set (map f xs)"
   by simp
 
 lemma project_set: