Ever wanted to write down symbols that make no sense to anyone else but you, or possibly an in-group of friends? Well, try $$+_{\textbf{on}} = \{ 0 | \textbf{oof} \} = \{0 \| 0 | \textbf{off} \}$$ for size. This class is an introduction to combinatorial game theory. CGT analyzes games by assigning numbers to positions and trying to figure out the arithmetic of games. While the starting ideas are simple, and the games we'll talk about will be simple, that doesn't mean that this introduction will be shallow! We'll need just a bit of imagination, a bit of whimsy, and a little bit of willingness to stretch your idea of what a 'number' is.