The pie rule, sometimes referred to as the swap rule, is a rule used to balance abstract strategy games where a first-move advantage has been demonstr

Pie rule - Wikipedia

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2021-06-18 04:00:08

The pie rule, sometimes referred to as the swap rule, is a rule used to balance abstract strategy games where a first-move advantage has been demonstrated. After the first move is made in a game that uses the pie rule, the second player must select one of two options:

The use of pie rule was first reported in 1909 for a game in the Mancala family.[1] Among modern games, Hex uses this rule.[2] Twixt in tournament play uses a swap rule.[3] The rule can be applied to other games which are otherwise solved for one player, such as Tablut.[4]

The rule gets its name from the divide and choose method of ensuring fairness in when dividing a pie between two people: one person cuts the pie in half, then the other person chooses which half to eat. The person cutting the pie, knowing the other person will choose the larger piece, will make as equal a division as possible.

This rule acts as a normalization factor in games where there may be a first-move advantage. In games that cannot end in a draw, such as Hex, the pie rule theoretically gives the second player a win (since one of the players must have a winning strategy after the first move, and the second player can choose to be this player), 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 switching places is worth the first-move advantage.

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