diff --git a/units/en/unit8/visualize.mdx b/units/en/unit8/visualize.mdx
index af05a571..fd977ca7 100644
--- a/units/en/unit8/visualize.mdx
+++ b/units/en/unit8/visualize.mdx
@@ -65,4 +65,4 @@ The final Clipped Surrogate Objective Loss for PPO Actor-Critic style looks like
 
 <img src="https://huggingface.co/datasets/huggingface-deep-rl-course/course-images/resolve/main/en/unit9/ppo-objective.jpg" alt="PPO objective"/>
 
-That was quite complex. Take time to understand these situations by looking at the table and the graph. **You must understand why this makes sense.** If you want to go deeper, the best resource is the article [Towards Delivering a Coherent Self-Contained Explanation of Proximal Policy Optimization" by Daniel Bick, especially part 3.4](https://fse.studenttheses.ub.rug.nl/25709/1/mAI_2021_BickD.pdf).
+That was quite complex. Take time to understand these situations by looking at the table and the graph. **You must understand why this makes sense.** If you want to go deeper, the best resource is the article ["Towards Delivering a Coherent Self-Contained Explanation of Proximal Policy Optimization" by Daniel Bick, especially part 3.4](https://fse.studenttheses.ub.rug.nl/25709/1/mAI_2021_BickD.pdf).