I did put in some boxes, and that helped with visually organizing the boards a little, but the presence of a box, even, tells you something: It tells you if that's an end-board state. I like that the tic-tac-toe comic didn't have a lot of extraneous stuff. RM: Yes, Tufte's real focus is always to convey the information with as little ink as possible. MH: It's so effcient, likeEdward Tufte's Visual Explanations book. It's a way to organize that makes it so you can quickly shade in, for example, all the wins for X, and you'll be able to see whether there are a lot of them or only a few. It seemed like there should be some way to present the data where making the choice is just zooming in on the grid or something, and I wound up doing what you see in the comic. I was trying to figure out if there was a way to present the information so that at every stage you are making a choice on a grid of nine possibilities. I did the calculations, and when I realized that for the full tree I would need a piece of paper that was bigger than the dining room table, I thought, I'm not drawing that!

RM: The full tree of possible moves would be a lot bigger than this. MH: What gave you the idea to present the information in this way? People have made these trees before, and some of them are quite complicated, but you managed to fit it all in one page. The thing that was interesting for me here was the moves that take into account psychology and the places that people are least likely to see that a win is forced. I was looking for moves where you can force a win, and you can do it in a way that isn't obvious. MH: So you wanted to go with a less common opening move? The reason I went for the upper-left opening move in this comic was that with this one, there are some winning moves that aren't the ones that everyone knows. Part of what started this off is that I had tried doing these maps when I was in English class in 11th grade, sitting there and working out a tree for most of tic-tac-toe, and I had sort of taken it as an article of faith that the best move for X is in the center.

With every opening move for X it's going to be a draw if you move optimally from that point onward. MH: How come you didn't start with X in the middle? There was no way I was doing the rest of it by hand! It took me something like 12 hours to draw out the fifth of it that I did.

I think I drew maybe a fifth or a sixth of the actual chart by hand, and then put that in the computer and mirrored and flipped it, and pieced together the rest of it. Randall Munroe: I remember that-I have a callus in my hand from making it. The only winning move is to play, perfectly, waiting for your opponent to make a mistake.

Xkcd by Randall Munroe