diff --git a/u2/list_ops.py b/u2/list_ops.py
index 4581d7e..f3ea299 100644
--- a/u2/list_ops.py
+++ b/u2/list_ops.py
@@ -4,6 +4,7 @@ def append(list1, list2):
         result = result + [x]
     for x in list2:
         result = result + [x]
+    return append
 
 def concat(lists):
     result = []