--- a/LamEx.thy	Fri Oct 30 14:25:37 2009 +0100
+++ b/LamEx.thy	Fri Oct 30 15:22:59 2009 +0100
@@ -78,7 +78,7 @@
   sorry
 
 lemma real_alpha:
-  assumes "t = ([(a,b)]\<bullet>s)" "a\<sharp>s"
+  assumes "t = [(a,b)]\<bullet>s" "a\<sharp>[b].s"
   shows "Lam a t = Lam b s"
 sorry