From 6f03e66c7830278666b256108b80e62fc10a0e32 Mon Sep 17 00:00:00 2001
From: Tianyi Cui <tianyicui@gmail.com>
Date: Sun, 28 Nov 2010 06:14:18 +0000
Subject: [PATCH] 56

---
 BinaryTrees.hs | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/BinaryTrees.hs b/BinaryTrees.hs
index 219661d..a80ceaf 100644
--- a/BinaryTrees.hs
+++ b/BinaryTrees.hs
@@ -15,3 +15,12 @@ cbalTree n =
     , ta <- cbalTree p
     , tb <- cbalTree q
     ]
+
+symmetric (Branch _ ta tb) = mirror ta tb
+symmetric _ = False
+
+mirror Empty Empty = True
+mirror (Branch _ t1a t1b)
+       (Branch _ t2a t2b) =
+    (mirror t1a t2b) && (mirror t1b t2a)
+mirror _ _ = False