Gokyo Shumyo, Section 1, Problem 23 / Solution

Tesuji  

The clamp at is the tesuji.

Main line  

With and stones added, lives. After , a and b are miai for White to get a second eye to the left or right of . prevents Black atari at c.

Variation 1  

After the sequence to , a and b are miai.

Variation 2  

If Black here, White makes two eyes and Black a or b don't work because of the presence of .

Variation 3  

After this sequence, White makes miai of a second eye at a or one at b in the corner.

Without the clamp  

Black can play at and gets the hane at . If White now clamps at a, it's too late.

Without the clamp, trying the capture as above  

Here White gets only one eye at . The stone at looked like a shapeful move, but ironically ended up giving away an eye for no reason. It's still too late for the clamp, because Black just connects, and if White tries to cut, the ladder doesn't work (moves -).

Naturally at , etc. leads to the mirror-image diagram (on the first three lines anyway).

This could be seen as another application of play on the point of symmetry, though in a perverse sense: since White's position has an even number of stones in each line, the position is symmetric but there is no point of symmetry to play on, suggesting that maybe White should try something else - in this case, the clamp.

At any rate, it appears that (of course) White should just follow up on the clamp if it's ignored, and run into the corner.

Failure at move 5 in the main line  

is a mistake. Black can kill with and . Then if , Black follows up with the connection tesuji at a.

Another try?  

Karl Knechtel: How should White respond if Black ignores the clamp?

This is my best reading for each of the circled alternatives:

Line 1 (9 at marked stone)  

That seems to make miai of a and b to cut, resulting in eyes at c and d, but maybe I'm missing better play for Black.

Line 1 Variation  

unkx80: Nice try, but why not play as in this diagram? In any case, White should always play Line 1 rather than Line 2 as white gains an entire corner.

I leave it to you to see that Black is captured.

Line 2  

That seems to leave eyes at a and , because Black must approach at b in order to take away the eye at and c seals it off. The throw-in at c doesn't appear to work either - even if that didn't put the marked stone in atari after White captures at b, Black can't prevent White from making the eye at , and three stones in front of a prevent the hane from stealing that eye.

But... in that case... since the clamp didn't come into play, why can't White play like this to begin with? I.e, play at a or above, and capture at or when Black applies pressure? Studying the "without the clamp" diagram further suggests that it's because playing there first tips White's hand; Black starts diagonally across (obviously, to avoid auto-atari) and after that, if White tries the capture, the EyeShape has been destroyed by playing at both points on the first line.

unkx80: Please also note that after White , White can play at d to capture the marked stone.

Problem 24
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