diff --git a/book/_toc.yml b/book/_toc.yml
index d2184e2..f5ebf5d 100644
--- a/book/_toc.yml
+++ b/book/_toc.yml
@@ -18,10 +18,13 @@ parts:
       - file: exercises/summary
     - file: exercises/advanced_exercises.md
       sections:
-      - file: type3.md
+      - file: exercises/type3.md
         sections:
         - file: exercises/007.md
         - file: exercises/008.md
+      - file: exercises/type4.mb
+        sections:
+        - file: exercises/009.md
     - file: references.md
     - file: changelog.md
     - file: credits.md
diff --git a/book/exercises/type4.md b/book/exercises/type4.md
new file mode 100644
index 0000000..e69de29