Fix2

u2/list_ops.py

@@ -9,7 +9,10 @@ def append(list1, list2):
 
 def concat(lists):
     result = []
+    if lists == []:
+        return []
     for i in lists:
+        if i != []:
             result += i
         return result
     """Spojí zoznamy obsiahnuté v lists do jedného zoznamu.
@@ -40,6 +43,8 @@ def length(seq):
 
 def map(function, seq):
     result = []
+    if seq == []:
+        return []
     for i in seq:
         a  = function(seq[i])
         result.append(a)