What is Taraguchi-10?
Taraguchi-10 is the opening rule of today's Renju World Championship. It shares the opening between both players, so neither can steer the game into a position known to win for one colour. Once the opening is over, normal renju takes over.
The first four stones go closer and closer to the centre: Black's first stone on the centre point, the second stone inside the central 3 × 3 square, the third inside the central 5 × 5 square and the fourth inside the central 7 × 7 square. Before the second, third and fourth stones, the player about to move may swap colours instead; the other player then holds that colour and plays the stone.
After the fourth stone, the player holding Black chooses how the fifth move is made. In the first choice, colours may be swapped once more, Black plays the fifth stone inside the central 9 × 9 square, and White may swap again before playing the sixth stone anywhere. In the second choice, Black offers ten fifth moves anywhere on the board, no two of them symmetrical; White picks one of them for Black and plays the sixth stone, with no further swap.
Rule changes
| Rule | Standard Renju | Taraguchi-10 |
|---|---|---|
| First stones | Standard RenjuBlack plays the first stone anywhere on the board, then the players take turns. | Taraguchi-10The first stone goes on the centre point, the second inside the central 3 × 3 square, the third inside 5 × 5 and the fourth inside 7 × 7. |
| Colour swap | Standard RenjuNot used: each player keeps the colour they start with. | Taraguchi-10Before each of the second to fifth stones, the player about to move may swap colours instead of moving. After a fifth stone played inside 9 × 9, White may swap once more. |
| Fifth move | Standard RenjuBlack plays the fifth stone anywhere. | Taraguchi-10Black either plays it inside the central 9 × 9 square, or offers ten fifth moves anywhere, no two symmetrical, and White picks the one that is 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. | Taraguchi-10The same, from the sixth stone on. Forbidden moves also apply to Black's stones and offered fifth moves during the opening. |
History
The Taraguchi rule was proposed by the Japanese player Yusui Yamaguchi as a development of the Tarannikov opening rule, and its name joins the two names. The Renju International Federation brought it in with the Soosõrv and Yamaguchi rules at its extra General Assembly in 2008, when it looked for successors to the RIF opening rule. It was used at European Championships from 2010, and in 2011 the federation certified the Taraguchi-N form, in which N is the number of fifth moves Black may offer.
Taraguchi-10 became the rule of the Team World Championship in 2024 and of the World Championship in 2025, replacing Soosõrv-8. The narrowing squares keep the first stones near the centre without fixing a list of openings, and the ten offered fifth moves make the second choice costly in any opening that is good for Black.