diff -r cc6969542f8d -r c46faf9762f7 src/HOL/Data_Structures/Lookup2.thy
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/HOL/Data_Structures/Lookup2.thy	Wed Sep 23 09:47:04 2015 +0200
@@ -0,0 +1,21 @@
+(* Author: Tobias Nipkow *)
+
+section \<open>Function \textit{lookup} for Tree2\<close>
+
+theory Lookup2
+imports
+  Tree2
+  Map_by_Ordered
+begin
+
+fun lookup :: "('a::linorder * 'b, 'c) tree \<Rightarrow> 'a \<Rightarrow> 'b option" where
+"lookup Leaf x = None" |
+"lookup (Node _ l (a,b) r) x =
+  (if x < a then lookup l x else
+   if x > a then lookup r x else Some b)"
+
+lemma lookup_eq:
+  "sorted1(inorder t) \<Longrightarrow> lookup t x = map_of (inorder t) x"
+by(induction t) (auto simp: map_of_simps split: option.split)
+
+end
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