I. INTRODUCTION  
A. Background  
B. Safety categorization in RL  
C. CBF methods in RL  
D. CONTRIBUTIONS  
E. ORGANIZATION  

II. PRELIMINARIES  
A. Control Barrier Functions  
B. Reinforcement learning  

III. SAFE REINFORCEMENT LEARNING  

IV. CBF CONSTRUCTION  

V. DISCUSSION  
A. MODEL-FREE VS MODEL-BASED  
B. Effect of safety on policy performance  
C. Challenges and limitations  

VI. CONCLUSION