diff --git a/deep-learning-intro-for-hep/_config.yml b/deep-learning-intro-for-hep/_config.yml
index d06712e..e986d76 100644
--- a/deep-learning-intro-for-hep/_config.yml
+++ b/deep-learning-intro-for-hep/_config.yml
@@ -1,4 +1,4 @@
-#######################################################################################
+######################################################################################
 # A default configuration that will be loaded for all jupyter books
 # See the documentation for help and more options: 
 # https://jupyterbook.org/customize/config.html
@@ -14,6 +14,7 @@ logo                        : logo.png  # A path to the book logo
 # See https://jupyterbook.org/content/execute.html
 execute:
   execute_notebooks: force
+  allow_errors: false
 
 # Define the name of the latex output file for PDF builds
 latex:
@@ -45,3 +46,4 @@ parse:
 sphinx:
   config:
     html_extra_path: ["img/tensorflow-playground.png"]
+    nb_execution_show_tb: true
diff --git a/deep-learning-intro-for-hep/universal-approximators.md b/deep-learning-intro-for-hep/universal-approximators.md
index d1e483c..64caa13 100644
--- a/deep-learning-intro-for-hep/universal-approximators.md
+++ b/deep-learning-intro-for-hep/universal-approximators.md
@@ -32,6 +32,10 @@ $$y = \left\{\begin{array}{l l}
 -1 + 3.5 x - 2 x^2 & \mbox{otherwise} \\
 \end{array}\right.$$
 
+```{code-cell} ipython3
+assert False
+```
+
 ```{code-cell} ipython3
 import numpy as np
 import matplotlib.pyplot as plt