diff -r b594e9277be3 -r 1335462046e8 src/HOL/Data_Structures/Tree23.thy
--- a/src/HOL/Data_Structures/Tree23.thy	Sun Nov 15 12:45:28 2015 +0100
+++ b/src/HOL/Data_Structures/Tree23.thy	Sun Nov 15 14:38:29 2015 +0100
@@ -10,9 +10,9 @@
 fixes height :: "'a \<Rightarrow> nat"
 
 datatype 'a tree23 =
-  Leaf |
-  Node2 "'a tree23" 'a "'a tree23" |
-  Node3 "'a tree23" 'a "'a tree23" 'a "'a tree23"
+  Leaf ("\<langle>\<rangle>") |
+  Node2 "'a tree23" 'a "'a tree23"  ("\<langle>_, _, _\<rangle>") |
+  Node3 "'a tree23" 'a "'a tree23" 'a "'a tree23"  ("\<langle>_, _, _, _, _\<rangle>")
 
 fun inorder :: "'a tree23 \<Rightarrow> 'a list" where
 "inorder Leaf = []" |