The surreal numbers are a number system (in fact, the largest ordered field of numbers) found within the structure of partisan games.

This is the fourth and final part in a miniseries on game theory. Watch the whole series here:    • Game Theory  

Sections:
0:00 Hackenbush
1:15 Advantages
3:10 Mixing colors
4:43 Towers
6:23 Set notation
7:27 Evaluation
9:20 Real numbers
10:59 Surreal numbers
12:59 Universal ordered field
14:15 Where next?