diff -r db0f4f4c17c7 -r d7ff0a1df90a src/HOL/Library/Permutation.thy
--- a/src/HOL/Library/Permutation.thy	Tue Jun 16 20:50:00 2015 +0100
+++ b/src/HOL/Library/Permutation.thy	Wed Jun 17 17:21:11 2015 +0200
@@ -136,7 +136,7 @@
   apply (erule perm.trans)
   apply (rule perm_sym)
   apply (erule perm_remove)
-  apply (drule_tac f=set_of in arg_cong)
+  apply (drule_tac f=set_mset in arg_cong)
   apply simp
   done