# Pie rule

## Book Suggestions: |

**pie rule**, sometimes referred to as the

*swap rule*, is a meta-rule commonly used in abstract strategy board games like Hex and Havannah. It can be stated as follows:

- After the first player makes their first move, the second player has the option of either:
- Letting the move stand, in which case they are the second player and move immediately, or
- Switching places, in which case they are now the first player, and the "new" second player now makes their "first" move. Effectively, the second player
*becomes*the first player, and it is as if that move was theirs, and the game is now proceeding.

This rule acts as a normalisation factor in games where there may be a first-move advantage; since Hex has a proof for a first-player win, the pie rule technically gives the second player a win (depending on their choice of switching or not), but the practical result is that the first player will choose a move neither too strong nor too weak, and the second player will have to decide whether the first move advantage is worth it.

The game of Orbit uses a "refined" pie rule, which technically has the "real" pie rule as a subset; like Hex being a subset of Y, however, the "refined" pie rule complicates matters considerably.

## References

- Browne, Cameron.
*Hex Strategy: Making the Right Connections*. ISBN 1-56881-117-9 - Meyers, Steven. "rules --- Orbit". http://home.fuse.net/swmeyers/orru.htm
- Schmittberger, R. Wayne.
*New Rules for Classic Games*. ISBN 0-471-53621-0