diff --git a/trees_and_graphs/preorder_transversal.py b/trees_and_graphs/preorder_transversal.py
index 09c26d5..9e2f7bc 100644
--- a/trees_and_graphs/preorder_transversal.py
+++ b/trees_and_graphs/preorder_transversal.py
@@ -1,3 +1,7 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+# author: bt3gl
+
 # recursive and iterative inorder traversal
 
 def preorder_recursive(root: Optional[TreeNode]) -> list[int]: