Yose Problem

British Go Journal No. 20. July 1973. Page 8.

J. T. Fairbairn

Problem

Question 1

Black to play. What is the result if correct yose are played?

Question 2

White to play. What is the result if correct yose are played?

Question 3

Count the number of points for each individual yose play.

Question 4

What is the largest move?

Question 5

What is the smallest move?

(Assume that there are no stones already captured by either side.)

Answers

Diagram 1 (Black to play)

• Black 1 is tesuji and obviously the largest move.
• White 6 cannot be omitted. The reason it cannot be one line higher is that black could then play the atekomi A.
• Black 7' should not here be at 12. Both points are gote but black 7 leaves the threat of going one point below 12.
• White can play the kikashi moves of 8 and 10 in sente.
• White 12 ispreferred to 13 or 14 because of the threat from black 7.
• Confirm that because of black's atekomi 15, white must later play B.
• White 18 is the last move.

Black's territory = 26 points,
White's territory = 26 points.
Result = jigo.

Diagram 2 (White to play)

• White 1 and 3 are kikashi. You should be aware of the necessity of playing all sente kikashi moves before playing the largest gote move in yose.
• Black 2 and 4 are inevitable. This black group would die if black were to turn to the large yose in the top left-hand corner.
• White 5 is the maximum gote yose. It s also big because it prevents black's sente yose of the previous diagram.
• Black 6 is sente.
• Black 8 and White 9 are also maximum moves.
• Black 14 is 1 point because it forces white A later.

When Black completes the game by taking the half-point ko at 18 and connecting at 11, his territory, including captured men, is 23 points and White's is 30.
Therefore White wins by 7.

Diagram 3 (Q3, 4 & 5)

• Black A is worth 8 points and therefore white B which prevents this is also worth 8. (This figure is obtained from the sum of the differences between Dia 1 and Dia 2.)
• C is worth 5 points, but if white answers immediately as in Dia 2, it is worth 2 points in sente.
• D is 2½ points, or in other words, if white continues 1 line further, black will have to take off white and fill in one point of his own teritory.
• E equals 1 point in sente because white can play to the left of E later.
• F is one point in sente, G 1 point in gote and H 2/3 point.

On the basis of the above calculations, the answers to questions 4 and 5 are:
Largest move, black A or white B;
Smallest move, yose H.