Source:
Problem diagram.
Black plays.
Segoe Kensaku & Go Seigen, Ishi Press
Solution follows
(or click here to download SGF)
Correct.
Everybody knows the clamp tesuji at 1. Right?
This problem is a great example of how this clamp can be
catastrophic for the "clampee", when the "clamper" has even a
minimum of nearby support.
You (as the "clamper") must always have a response ready for a White descent at 2.
Otherwise, don't play the clamp!
Every situation is different, but in this position, Black 3 is the killer move.
Black 7 cuts off the White group.
And even though White 10 can capture Black 1,
White's one-eyed group will lose the semeai after Black 11.
White collapses.
White fallback.
When White cannot descend, White 2 is the usual fallback strategy.
But with the Black stone above, White has to meekly extend at 8.
But then Black can keep forcing with 9.
White must extend at 10 or Black will play there and destroy almost all of White's territory.
In any event, Black has already destroyed almost half of White's territory, and in sente!
White variation.
Trying to block Black with 4 is dangerous.
After 7, if Black wins the ko, almost all of White's territory evaporates.
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