diff --git a/README.md b/README.md
index 927449a..0b971a8 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,7 @@
 # php-monad
 📦 Implemented the concept of monads in functional programming in PHP.
+
+# references
+- https://zenn.dev/pixiv/articles/f109b02aa9d4e0
+- https://doc.rust-lang.org/std/option/enum.Option.html
+- https://doc.rust-lang.org/std/result/enum.Result.html