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The following is working code validating a Binary Search Tree in Python.
SNIPPET
1class Solution:
2 def is_valid_bst(self, root):
3 output = []
4 self.in_order(root, output)
5
6 for i in range(1, len(output)):
7 if output[i-1] >= output[i]:
8 return False
9
10 return True
11
12 def in_order(self, root, output):
13 if root is None:
14 return
15 ____________________________________
16 output.append(root.val)
17 self.in_order(root.right, output) Write the missing line below.
