1 Introduction  
1.1 Evolution towards provably safe RL  

2 Conceptual analysis  
2.1 Action replacement  
2.2 Action projection  
2.3 Action masking  
2.4 Impact on the distribution of actions  
2.5 Learning tuples  

3 Literature review  

4 Experimental comparison  
4.1 Environments  
4.2 Computation of the safe state set  
4.3 Results  

5 Discussion  

6 Conclusion