What is Gomoku with the Swap opening?
The Swap opening is a way to take the first-move advantage out of Gomoku. The first player does not just play Black. Instead they place three stones anywhere on the board: two black and one white. Then the second player looks at the position and chooses to play Black or White.
After the choice, White places the fourth stone and the game goes on as usual, one stone at a time. The player who set up the stones becomes whichever colour the other player did not take.
The idea is the old "I cut, you choose" rule. If the first player builds a position that is too good for Black, the opponent takes Black; if it is too weak, the opponent takes White. So the fairest thing to do is to place a balanced position. The winning rule does not change: in standard Gomoku you still need exactly five in a row. You can also use the Swap opening with Freestyle, Caro and Omok.
Rule changes
| Rule | Standard Gomoku | Gomoku with the Swap opening |
|---|---|---|
| First stones | Standard GomokuBlack places one stone, then the players alternate. | Gomoku with the Swap openingThe first player places three stones at once: two black and one white. |
| Choosing colours | Standard GomokuThe first seat plays Black for the whole game. | Gomoku with the Swap openingThe second player chooses Black or White after seeing the three stones; the first player takes the other colour. |
| After the opening | Standard GomokuWhite answers Black's first stone. | Gomoku with the Swap openingWhite places the fourth stone, and the players then alternate as usual. |
| How to win | Standard GomokuMake an unbroken line of exactly five stones. | Gomoku with the Swap openingThe same; the opening changes only who plays which colour. |
History
Swap rules come from the age-old way of sharing a cake fairly: one person cuts, the other chooses. Game designers use the same idea in many games, Hex being a famous example, to cancel the advantage of moving first.
In Gomoku the first player's edge is very large, and in 1994 Victor Allis proved that the first player wins Freestyle on an empty 15×15 board with perfect play. The Swap opening, with two black stones and one white placed by the first player, became a common answer to that problem. In 2009 tournament Gomoku moved to Swap2, which adds a third option for the second player, but plain Swap is still played as the quicker and simpler opening.