diff --git a/u6/matching_brackets.py b/u6/matching_brackets.py
index 57a00b3..0fe1e7d 100644
--- a/u6/matching_brackets.py
+++ b/u6/matching_brackets.py
@@ -1,4 +1,6 @@
 def is_paired (input_string):
+    pairs = {")": "(", "]": "[", "}": "{"}
+    stack = []
     for char input_string:
         if char in opening:
             stack.append(char)