diff --git a/trees_and_graphs/construct_tree_inorder_postorder.py b/trees_and_graphs/construct_tree_inorder_postorder.py
index a1fec27..144779d 100644
--- a/trees_and_graphs/construct_tree_inorder_postorder.py
+++ b/trees_and_graphs/construct_tree_inorder_postorder.py
@@ -1,25 +1,29 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+# author: bt3gl
 # Given two integer arrays inorder and postorder where inorder is the inorder 
 # traversal of a binary tree and postorder is the postorder traversal of the
 # same tree, construct and return the binary tree.
 
-def build_tree(inorder: list[int], postorder: list[int]) -> Optional[TreeNode]:
-        
-        def fill_tree(i_left, i_right, inorder_map):
+
+def fill_tree(i_left, i_right, inorder_map):
             
-            if i_left > i_right:
+        if i_left > i_right:
                 return None
             
-            val = postorder.pop()
-            root = TreeNode(val)
+        val = postorder.pop()
+        root = TreeNode(val)
 
-            index_here = inorder_map[val]
+        index_here = inorder_map[val]
 
-            root.right = fill_tree(index_here + 1, i_right, inorder_map)
-            root.left = fill_tree(i_left, index_here - 1, inorder_map)
+        root.right = fill_tree(index_here + 1, i_right, inorder_map)
+        root.left = fill_tree(i_left, index_here - 1, inorder_map)
             
-            return root
+        return root
+
+
+def build_tree(inorder: list[int], postorder: list[int]) -> Optional[TreeNode]:
 
         inorder_map = {val: index for index, val in enumerate(inorder)}
-  
         return fill_tree(0, len(inorder) - 1, inorder_map)