diff --git a/Book4_Ch01_Python_Codes/Bk4_Ch1_05.py b/Book4_Ch01_Python_Codes/Bk4_Ch1_05.py
deleted file mode 100644
index 4dba95d..0000000
--- a/Book4_Ch01_Python_Codes/Bk4_Ch1_05.py
+++ /dev/null
@@ -1,17 +0,0 @@
-
-###############
-# Authored by Weisheng Jiang
-# Book 4  |  From Basic Arithmetic to Machine Learning
-# Published and copyrighted by Tsinghua University Press
-# Beijing, China, 2022
-###############
-
-# Bk4_Ch1_05.py
-
-import numpy as np
-
-# define a column vector
-a = np.array([[2], [2]])
-
-b = 2*a
-c = -1.5*a