diff --git a/20.01. Programming/Prompting.md b/20.01. Programming/Prompting.md
index 9acdc69..2e82c57 100644
--- a/20.01. Programming/Prompting.md	
+++ b/20.01. Programming/Prompting.md	
@@ -18,5 +18,13 @@ Add docstring in English to each classes and functions.
 編譯環境: Visual Studio 2022
 Python 版本： 3.12
 
+# Create global mutex
+Use `ctypes` and Win32Api `CreateMutex` to create a global mutex here. Use class to wrap it.
+This mutex shoid has these features:
+1. When user instantiate this class, use Win32api `OpenMutex` to try to open this global mutex, because this mutex mybe alreday created in another process.
+2. if `OpenMutex` failed, use `CreateMutex` to create the global mutex.
+3. this class should provide lock and unlock function, use `WaitForSingleObject` and `ReleaseMutex` to implement it.
+4. And, very important, class should has `release` function of mutex.
+
 
 # 參考來源
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