On the subject of topology, my game of choice is Sprouts, invented by mathematicians John Horton Conway and Michael S. Paterson at Cambridge University in 1967 (as a general rule, you can't go wrong with a game if Conway had anything to do with it).I was thinking about sprouts the other day and a few variations occurred to me. I don't know if they're particularly playable or if they add any interesting aspects to the game, but if you can't put a half-baked idea in a blog, what's a blog for?

The rules are simple:

1. Start with some dots on the paper. The more dots you have the longer the game takes so you will probably just want to start with two or three.

2. Players take turns either connecting two of the dots with lines or drawing a line that loops back and connects a dot with itself.

3. The lines can be straight or curved but they can’t cross themselves or any other lines.

4. Each dot can have at most three lines connecting it

5. When you draw a line put a new dot in the middle.

6. The first player who can’t draw a line loses.

Variant 1 -- Free sprouts

Played as above but with the following addition: for the first k moves of a game with n dots, the player, after drawing a line, adds a new dot.

Topologically the result is a game with n+2k dots (keep k small) but with the complication that lines are being drawn without knowing exactly how those lines partition the surface. This is still a game of perfect information but the variation should make it more difficult to think a few moves ahead.

Variant 2 and 3 -- Scored sprouts

Each player starts with a separate sheet of paper and proceeds to connect the dot according to the standard rules. After no more lines are possible, the players score their graphs based on the number of dots.

Score = 6

Score = 7

Score = 6

Score = 7

In variant 1 the player with the highest score wins. In variant 2, the win goes to the lowest.

Also posted at Observational Epidemiology.