The rules start with tic-tac-toe, but you have an account of play points. The first player gets one point; every subsequent turn a player gets two points. It costs two points to play on an edge square, three to play on a corner, and four to play in the center (i.e. it costs one point per tic-tac-toe that could be made through that square). You can make a play that makes your account go negative, but you need a positive account to play. Even if you have the points to play, you may pass on your turn and keep the points.
Here's an example game:
- Alice goes first, gets one point, and plays in the center. That costs four points, so her balance is negative three.
X Bob's points: 0 Alice's points: -3
- Bob gets two points and plays on the left side. That costs two points, so his balance goes back to zero.
O X Bob's points: 0 Alice's points: -3
- Alice gets two points, bringing her balance to negative one; that's not above zero, so she can't play.
O X Bob's points: 0 Alice's points: -1
- Bob plays in the corner, which costs three points, bringing his balance to negative one.
O X O Bob's points: -1 Alice's points: -1
- Alice gets two points, bringing her balance to one, so she can play on the corner (cost three) to block Bob.
X O X O Bob's points: -1 Alice's points: -2
- Bob plays in the corner, which costs three points, bringing his balance to negative two.
X O X O O Bob's points: -2 Alice's points: -2
- Alice's balance goes to zero, which isn't positive, so she can't play to block Bob.
X O X O O Bob's points: -2 Alice's points: 0
- Lucky for her, Bob also can't play: on his turn, his balance goes to zero.
X O X O O Bob's points: 0 Alice's points: 0
- Now Alice gets two and plays on the bottom to block Bob, returning her balance to zero.
X O X O X O Bob's points: 0 Alice's points: 0
- Bob plays on the top.
X O O X O X O Bob's points: 0 Alice's points: 0
- Alice sees she can't win, so she passes, keeping her two points.
X O O X O X O Bob's points: 0 Alice's points: 2
- Bob plays on the right.
X O O X O O X O Bob's points: 0 Alice's points: 2
- Alice is forced to play at the top.
X O X O X O O X O Bob's points: 0 Alice's points: 1
- That's a cat's game, but with a small differentiator: Alice has a remaining balance of one and Bob has a balance of zero, so Alice wins.