About Approach-Move Liberties (2009)
[ Territorial consequences of White's Atari ]
We will explain now, why White can profit territorially, if she does not play the optimal semeai move , when answering Black's kikashi in the bamboo joint. It's all about the connection of the two hasami-tsuke stones . Here, with White choosing the "correct" semeai move, Black is able to connect both of the hasami-tsuke stones. Even thereafter, his group has six liberties left (), which means that it had seven liberties in the very beginning. |
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However, if White had chosen the atari of - sub-optimal with regard to the semeai itself - Black could not save his endangered stone with a move at . If he did, as shown here, he had his group reduced to six liberties (5 * , ), which is one liberty too less. White will choose the Punishment Semeai, easily winning the game. Please note that it is safe for Black to connect at , after White captured at 0d, to reduce his loss to only one stone. |
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///: In conjunction with the guzumi (), Black now possesses four potential approach-move liberties . These four potential liberties will become three real liberties for Black. As before, "" marks the liberty that Black would gain through the kikashi of Michael Redmond in the bamboo joint, if White answered with the atari. |
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White needs nine moves (with the atari of supposed) to take Black's group off the board, one more move than without guzumi. In total (guzumi, hasami-tsuke, and atari), Black has won two liberties. However, please remember that Black is two moves behind in the Main Semeai of the problem - and so needed three more liberties for his group in the upper right. Therefore, two additional liberties for this group do not really benefit Black, and there will result no decisive consequences on the solution. If White connected at with , instead, she also needs one more move than without guzumi (eight moves in this particular case). Please note that from here on, we assume that White will answer Black's kikashi ( here) with the atari ( here). |
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///: The two additional liberties, mentioned above, result in a decisive difference, concerning Black's hasami-tsuke stones . The guzumi enables Black to connect both of this stones - after White's atari. After this, Black's group still has seven liberties ... |
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... - as many as without either the guzumi, or the hasami-tsuke. |
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///: But without the guzumi, Black cannot afford to connect with . This connection leaves him with only six liberties (), one liberty too less. There is only one potential approach-move liberty (), which does not help here. Therefore, Black must let White capture . |
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///: This territorial loss, compared to the marked guzumi exchange, leads us to the explanation, why Black's potential liberty in the Bamboo is a special one, and with a side-effect, in Igo Hatsuyōron 120. |
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Let us assume that Black's kikashi in the bamboo joint is played in a moment, when it is sente. Here, White answers with the atari of , to gain territorially. However, connecting the hasami-tsuke stone with a move at now would be gote for Black. In the problem, it will be difficult for Black to find a suitable moment to do so. |
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Therefore, it is likely that White will capture with . Black is able to connect at , because his group is still left with seven liberties (5 * , , 1 * ). White gained four points (, ) of territory in the corner. |
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///: Here we show that it is safe for Black to connect his hasami-tsuke stone - if he finds the opportunity to do so. After , he is still left with seven liberties (4 * , , 2 * ). In the problem, Black can play at , only if he did not answer a White move elsewhere on the board. Consequently, he will suffer a loss there - we suppose of at least three, maybe four, points - when White plays tenuki here, with . |
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If White had played tenuki, with , in the previous diagram, it makes no sense for Black to use his just won move for a reduction of White territory around his group in the top right corner. After , while Black's group still has seven liberties (4 * , , 2 * ). However, this one-point gain costs Black his additional liberty, so the liberties in the Main Semeai are par again. If White chooses the Semeai Variation, the stone that Black has just added to his group will become an additional prisoner, and will add to the points, White got elsewhere for her earlier tenuki in the corner. | |