diff --git a/course/lecture/lecture2.md b/course/lecture/lecture2.md
index 8af14b261e4a64239e4333dc8f25185bca162899..19e135f7c2ae0d2afb4297483b7a5e2592e8977c 100644
--- a/course/lecture/lecture2.md
+++ b/course/lecture/lecture2.md
@@ -5,6 +5,10 @@
 
 ------
 
+[Part I](lecture1.md)
+
+------
+
 **_Contents_**
 
 [[_TOC_]]