diff --git a/u2/list_ops.py b/u2/list_ops.py
index b351eab..252486a 100644
--- a/u2/list_ops.py
+++ b/u2/list_ops.py
@@ -4,4 +4,14 @@ def append(list1, list2):
         result = result + [item]
     for item in list2 :
         result = result + [item]
-    return result
\ No newline at end of file
+    return result
+def concat(lists):
+    result = []
+    for item in lists
+        result = append(result, item)
+    return result
+def filter(function, list):
+    res = []
+    if function(item) :
+        res = res + item
+    return res