1. Max Min Max Min Starting node and labels Figure 4.20 (pp. 153) Alpha-Beta Prune

2. Max Min Max Min Perform a DFS

3. Max Min Max Min Continue the DFS

4. Max Min Max Min 23 Until reach the depth we want, i.e., 3-ply in this case

5. Max Min Max Min 23 3 Propagate leaf values backward

6. Max Min Max Min 23 3 3

7. Max Min Max Min 23 3 3 3

8. Max Min Max Min 23 3 3 3Alpha Node Beta Node

9. Max Min Max Min 23 3 3 3Alpha Beta 5 New DFS path Ended with 5

10. Max Min Max Min 23 3 3 3Alpha Beta 5 5 Propagate backward

11. Max Min Max Min 23 3 3 3Alpha Beta 5 5 Because 3 < 5 The branch is pruned. Beta-Prune

12. Max Min Max Min 23 3 3 3Alpha Beta 5 5 New 3-ply DFS Ended with 0 0

13. Max Min Max Min 23 3 3 3Alpha Beta 5 5 0 0 Propagate backward

14. Max Min Max Min 23 3 3 3Alpha Beta 5 5 0 0 Propagate backward 0

15. Max Min Max Min 23 3 3 3Alpha Beta 5 5 0 0 The branch is cut off Because 3 > 0 Alpha Prune 0