1 files changed, 7 insertions, 0 deletions

diff --git a/ws2015/FFP/blaetter/03/FFP_U03_Funktoren.hs b/ws2015/FFP/blaetter/03/FFP_U03_Funktoren.hs
index 51ab9e5..935f9eb 100644
--- a/ws2015/FFP/blaetter/03/FFP_U03_Funktoren.hs
+++ b/ws2015/FFP/blaetter/03/FFP_U03_Funktoren.hs
@@ -184,3 +184,10 @@ instance Eq a => Eq (Options a) where
 
 instance Ord a => Ord (Tree a) where
   compare (Node x xs) (Node x' xs') = compare x x' `mappend` compare xs xs'
+    where
+      -- Siehe Data.Monoid
+      mappend LT _ = LT
+      mappend EQ EQ = EQ
+      mappend EQ LT = LT
+      mappend EQ GT = GT
+      mappend GT _ = GT