diff --git a/book/_toc.yml b/book/_toc.yml
index 14e8c2e68fe149b0429b9f69dcfc86506a58805a..2f0c3ca6c2943fa8555f59f34bd6b8c8f5c3572c 100644
--- a/book/_toc.yml
+++ b/book/_toc.yml
@@ -191,11 +191,13 @@ parts:
         - file: time_series/exercise4.ipynb
       - file: time_series/arma
         title: "AutoRegressive Moving Average (ARMA) process"
-    # START REMOVE-FROM-PUBLISH
+        sections:
+        - file: time_series/exercise5.ipynb
       - file: time_series/forecasting
         title: "Time Series forecasting"
       - file: time_series/optional
         title: "Supplementary material"
+    # START REMOVE-FROM-PUBLISH        
       - file: time_series/notebook
         title: Notebook
     - file: optimization/overview