diff --git a/book/contents/macro/intro.md b/book/contents/macro/intro.md
index 1818a761..ff0f8751 100644
--- a/book/contents/macro/intro.md
+++ b/book/contents/macro/intro.md
@@ -1 +1,3 @@
-# macro
\ No newline at end of file
+# macro
+
+https://www.reddit.com/r/rust/comments/s3mm8m/macro_hygiene/
\ No newline at end of file