MostDifficultProblemEver/Shuko's Solution

This is the solution as it was given by Fujisawa Shuko in 1982. Newer research has since made this somewhat outdated, although many sequences given here are still valid.

Solution 1-10  

B1 threatens to capture the lower right white group in an oiotoshi with a move at a. W2 prevents this, after which B3 connects to prevent white from capturing two black stones and connecting her groups

With W4 through W8, white defends her group on the right while attack black there. B5 through B9 prevent white from connecting, but must allow the cut W10

Solution 11-20  

With W12, white prevents the black group on the right from connecting. B13 is atari, giving black sente. With B15 through B19, black destroys white's eyeshape, making a temporary seki between the two groups on the right.

This seki will only last if the white group in the lower right corner does not die. As it cannot live independently, white must try to prevent black from forming two eyes in the lower right.

Solution 21-30  

With B21, black threatens to make two eyes for his group. W22 does the same for the white group in the lower right, and with B23 and W24, both players prevent the opponent from making two eyes. Thus, for now, another seki is born, this time between the groups in the lower right.

With B25 through B29, black starts an attempt to escape. White cannot block black, because black would then capture at a. And if black captures, white must play at W24 again to prevent black from living. But after each of the moves B25, B27 and B29, white would not have time to play at W24 because she would get cut (at 26, 28 and 30 respectively. White has no choice but to comply with blacks escape, falling back constantly so as not to give black any opportunities.

Solution 31-40  

With B31 through B37, black continues the pattern. On each move, white is unable to black, because she would not have time to play white+circle if black captures at a.

With B39 black stubbornly keeps walking out, because escape would mean the death of the white group in the lower right, and since that would also lift the seki on the right, it would make most of the right side black territory. White has no choice but to keep chasing black with W40

Solution 41-50  

Black keeps running, and white keeps chasing him. Allowing black to bend to the left would means escape or death. This is because a is still sente for black, requiring a response at white+circle. But after that, black would cut in the center and then play b, which kills to white group at the bottom.

Solution 51-60  

With B51, and B53, black again threatens to cut, and white is forced to defend. White cannot allow black to capture at W58 either, because this would result in a ko that white cannot win. Thus the chase continues.

Solution 61-70  

B65 and W66 are stunning moves. The entire central black chain is in atari! Why does black cut? Why doesn't white capture? It turns out that the situation is a rare example of a hanezeki position. If white captures at a, and black takes back at black+circle, then white must play white+circle to prevent black from forming two eyes. But the exchange has given black the single extra liberty he so desperately needs to lift the seki in the lower right.

So white is left with no other option than to leave the black chain on the board. But after B67, white is cut, and so must live at the bottom with W68.

With B69, and W70, black shifts his attack to the white group on the left. Capturing these would connect the central black chain to the left.

Why white cannot capture [see diagram to the right]

If white takes the central chain (at W4), black will take back at B1. White must play W2, but with B3, black starts approaching the group on the right. After B5, white is in atari and must capture with W6. B7 is at black+circle, and after the W8 B9 exchange, white is one liberty short.

from Cassandra:

Dia. Solution 21-30: Black is 1 point better if he exchanges Black S11 for White R12 before Black 21.

Dia. Why White cannot capture: White CAN play this sequence about 60 moves later (White 8 captures Black 1 in Sente). It remains true that she cannot capture the big Black group in the top right, but she gets an advantage of 4 points in this area (the captured Black stone plus 3 points of territory that Black will not get any more). So a 3-point-win for Black reverts into a 1-point-win for White.

And the most difficult problem ever remains unsolved !

MostDifficultProblemEver/Shuko's Solution last edited by on March 21, 2016 - 07:29
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