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JBS Solution
    Keywords: Problem

[Diagram]
Black to play.

Post your solution here.



HolIgor: I won't post a solution yet. In fact I am amazed at the level of this problem. Could it be dan level? We have not heard from our dans yet.

I lost it in an IGS game. I agreed gladly to this position considering it a sure win for Black. But it proved to be much more difficult than expected. So, I decided that Black loses here.

- Perhaps I should have added I'm a European 2 dan. Goran

When I opened a book at a random diagram I could not believe my eyes. Is it possible for Black to win?

Some general words about the solution. The motifs are normal: a group with an eye wins agains a group without eyes, hence some eye stealing, a sacrifice to gain a tempo, shortage of liberties. But everything requires exact reading.


[Diagram]
How about a ko? (9 at 1)

Goran

HolIgor: Black can do better.


[Diagram]
Black 1?

MortenPahle:

I'm not sure of the best 'defence' for White, but I cannot see any quick way for White to save his stones after B1...?


[Diagram]
Black 1 fails

White rebuts this with a simple outside attack true to the fundamentals. HolIgor

Oops. I thought Black could cut one to the left of W6, but he cannot.



DaveSigaty: I couldn't figure this one out. Finally I gave up and searched my books for an analysis - I wasn't even close to finding the key play (which is Black's second play rather than his first!). The honor of posting the answer belongs to HolIgor when he is ready.


[Diagram]
My attempt

Before HolIgor does so, allow me to make a try... After B7, White clearly is one move behind.


[Diagram]
Better defense (Black 11 at a, White 12 at b)

A better defense for White seems to be W2 here. After White 12, Black loses despite the me ari me nashi.


[Diagram]
Improvement

Black however has an improvement with B7 here. First destroying the eye, then moving out seems to be enough to save Black.


[Diagram]
No good either

Playing W6 on this side does not work either. After B7, the best White can do is to capture B5 in sente.


[Diagram]
Last defense?

One more line of defense seems open for White, namely W4 here. But the B5 - W6 exchange again saves the day. If White plays Wh6 at a, Black plays at W6, and gains liberties again.

-- AndreEngels


[Diagram]
White's defense?

I hate disagreeing with stronger players, but how does Black play after W6 here? Black must defend against White a. Black at b gives White d and Black dies.

Black at a gives White c and Black dies. Black at e again gives White c and Black suffers? -- MortenPahle

You should not hate disagreeing with me. Certainly not when, as in this case, you are right and I am wrong. -- AndreEngels

HolIgor: The move proposed by Morten is a strong defence but Cho shows how to beat it. Consider it a new problem.


[Diagram]
Black wins still!

[Diagram]
Black e, White c Black 3?

Goran

Yes, Black sacrifices two stones but kills the rest. --HolIgor



Thus the first move is found:

[Diagram]
Black 1 is the first move.

White's strongest defence is W2. So the problem is to find Black's second move; which is the key, as Dave put it.

-- HolIgor



[Diagram]
Black 1 seems to work

Goran

Yes, this is the solution. The variations should be considered further:

JBS final solution.



[Diagram]
Alternative solution?

dnerra: I just looked at this problem and read out this simple-minded sequence. It looks so obvious that it might be worth discussing: What did I miss in this sequence?


[Diagram]
Tesuji

Apparently, W1 in this diagram is the only move here. (White a, Black b, White 1, Black c should usually be very good for Black, as White has to come back and make life at d.



HolIgor

[Diagram]
Tesuji

The usual tesuji in such cases is this Wh1. I give only one variation. But one has to be very careful.

The problem is very good. It was published more than a half millenium ago.



This is a copy of the living page "JBS Solution" at Sensei's Library.
(OC) 2004 the Authors, published under the OpenContent License V1.0.