diff --git a/academic_codes/2021.03.19_plot_twist_graphene_with_python/twist_graphene.py b/academic_codes/2021.03.19_plot_twist_graphene_with_python/twist_graphene.py
index b03b8ff..318f4f6 100755
--- a/academic_codes/2021.03.19_plot_twist_graphene_with_python/twist_graphene.py
+++ b/academic_codes/2021.03.19_plot_twist_graphene_with_python/twist_graphene.py
@@ -3,7 +3,6 @@ This code is supported by the website: https://www.guanjihuan.com
 The newest version of this code is on the web page: https://www.guanjihuan.com/archives/10909
 """
 
-from types import coroutine
 import numpy as np
 import copy
 import matplotlib.pyplot as plt