What is Soosõrv-8?
Soosõrv-8 is the opening rule the Renju World Championships used from 2017 to 2023. The first player sets up one of the 26 standard openings, and the other player then decides how many fifth moves Black must offer. Once the opening is over, normal renju takes over.
The first player places three stones: Black on the centre point, White inside the central 3 × 3 square and Black inside the central 5 × 5 square. Up to symmetry these give exactly 26 openings. The other player may now swap colours. Whoever holds White then plays the fourth stone anywhere and declares a number from 1 to 8.
The player holding Black may swap once more, then offers that many fifth moves, no two of them symmetrical. White picks one of them for Black and plays the sixth stone. If only one fifth move was declared, Black simply plays it.
Rule changes
| Rule | Standard Renju | Soosõrv-8 |
|---|---|---|
| First stones | Standard RenjuBlack plays the first stone anywhere on the board, then the players take turns. | Soosõrv-8The first player places the first three stones: Black on the centre point, White inside the central 3 × 3 square and Black inside the central 5 × 5 square. |
| Fourth move | Standard RenjuWhite plays the fourth stone anywhere. | Soosõrv-8White plays the fourth stone anywhere, then declares how many fifth moves Black must offer, from 1 to 8. |
| Colour swap | Standard RenjuNot used: each player keeps the colour they start with. | Soosõrv-8The other player may swap colours after the third stone, and the player holding Black may swap again after the declaration. |
| Fifth move | Standard RenjuBlack plays the fifth stone anywhere. | Soosõrv-8Black offers the declared number of fifth moves, no two symmetrical, and White picks the one that is played. A single declared fifth move is simply played. |
| After the opening | Standard RenjuBlack may not make a double three, a double four or an overline. Black wins with exactly five in a row, White with five or more. | Soosõrv-8The same, from the sixth stone on. Forbidden moves also apply to Black's stones and offered fifth moves during the opening. |
History
The rule was proposed by the Estonian player Ants Soosõrv. It was the official opening rule of the 2008 European Renju Championship, the year the Renju International Federation's extra General Assembly approved it together with the Taraguchi and Yamaguchi rules. In its first form White could declare up to four fifth moves. In 2011 the federation certified Soosõrv-N, proposed by the Russian Renju Association, in which the upper limit N can vary.
In 2015 the General Assembly chose Soosõrv-8 for the World Championship from 2017. It was played there in 2017, 2019 and 2023, and at the Team World Championship in 2018, before Taraguchi-10 replaced it in 2024 and 2025.