diff --git a/08-vyrazy/objektove2.py b/08-vyrazy/objektove2.py
index 6295851f5cfb56370a21b1210cb6514240706a09..e7310585101f6e6e697b7011e81147d4cbb7937a 100755
--- a/08-vyrazy/objektove2.py
+++ b/08-vyrazy/objektove2.py
@@ -30,6 +30,8 @@ class NumNode(Node):
 
 class BinaryNode(Node):
 
+    op_name = '?'
+
     def __init__(self, left, right):
         self.left = left
         self.right = right
@@ -40,6 +42,9 @@ class BinaryNode(Node):
     def eval(self):
         return self.eval_op(self.left.eval(), self.right.eval())
 
+    def eval_op(self, x, y):
+        raise NotImplementedError()
+
 
 class AddNode(BinaryNode):