diff -r 289728193164 -r 698967eceaf1 thys/ReStar.thy
--- a/thys/ReStar.thy	Wed Mar 02 14:35:50 2016 +0000
+++ b/thys/ReStar.thy	Thu Mar 03 08:22:39 2016 +0000
@@ -29,7 +29,7 @@
 definition
   Der :: "char \<Rightarrow> string set \<Rightarrow> string set"
 where
-  "Der c A \<equiv> {s. [c] @ s \<in> A}"
+  "Der c A \<equiv> {s. c # s \<in> A}"
 
 lemma Der_null [simp]:
   shows "Der c {} = {}"