diff --git a/http-delete-mutex/readme.md b/http-delete-mutex/readme.md
index fed76da..629c217 100644
--- a/http-delete-mutex/readme.md
+++ b/http-delete-mutex/readme.md
@@ -1,21 +1,23 @@
 # rgncycle-libulfius
+## general
 
 libulfius API for rgncycle
 
 * build
-
 ```
 make
 ```
 
 * run
-
 ```
 ./main
 ```
 
 * run Valgrind tool `Memcheck`
-
 ```
 valgrind --leak-check=yes -s ./main
 ```
+
+## links
+
+* [mutex in c](https://www.delftstack.com/howto/c/mutex-in-c/)