Capture go problems ⚫

[antonTobi]

I made some diagrams to make it easier for other people to follow along the solution:

Problem 3 solution

It might look like white is winning, since both sides have 4 “territory” and it is black to move. But white’s territory is defective (C1 and D2 are miai) so this is actually winning for black.

If white tries to cut with 2, white dies first. In normal go white would have the snapback at B1, but in capture go A1 is a real eye.

I think the next one might be sligthly easier:

Problem 4:

Demo board

[belabacsijolvan]

I like capture go because if you have no board you can play it on paper.

My guess

The first move must be B2.
Whites best choice is C2.
Black must C1.
White C3 is trivially bad, so white A4.
Black A2.
White cannot snapback so black wins.

[antonTobi]

You got it, well done!

[antonTobi]

Problem 5

Demo board

[Jhyn]

(Forums go too fast, I have to come down a lot to find the thread)
I found the same as belabacsijolvan for Problem 4

My idea for Problem 5

This looks like black can win this by straightforward territory, but the natural D3 fails. A 5x5 yose problem! I suggest A3.
If A4 A2 B4 D3 D4 E3 E4 Black wins by one.
If D2 we answer D4! After that:

• D3 B4 C4 C5 E4 D5 etc., Black wins
• In other variations, we essentially cut at D3 as soon as we can and capture the lonely stone.

If D3, B4, and then either D2 D4 or C4 D2 and Black wins

No! I found out about A3 D2 D4 A4 A2 B4 and Black is in trouble. I’ll edit the post after I find more.

[antonTobi]

On the right track! Your variation and why it doesn’t work is kind of more interesting than the correct variation

[antonTobi]

Since @Jhyn already found the correct first move, and the rest of the solution isn’t that interesting, I’ll go ahead and show it below.

Problem 5 solution

After W D2, black can simply hane at D1 (B4 directly would also work). You can see what I mean by the D4-variation being more exciting! It makes for a good new problem:

Problem 5b: How should black respond?
The only winning sequence is the one Jhyn found above. (Edit: Actually, black can start with either A4 or B4. The idea is the same, just a slightly difference order of moves)

Problem 6 is on an even bigger board (still small by normal standards of course ), but the reading involved is probably easier than the last one. On bigger boards the game becomes more similar to normal go.

Problem 6

Demo board

[belabacsijolvan]

not a solution, but spoiler

I’m getting pretty sure, that you cannot avoid this state of the board:

edit: I was wrong. it leads to defeat and you can avoid it.

[belabacsijolvan]

solution?

I was wrong. I found the following sequence:

and then this kills either C3 or D4:

The takeaway message is avoid the swastika! (or any symmetric state)

[antonTobi]

You got it!

I’ll continue the theme of increasing the board size, since I find it satisfying that problem 7 is on a 7x7-board The next problem after this will probably be on a smaller board again.

Problem 7

Demo board

[belabacsijolvan]

Thanks for posting these! They are really cool, and they show some concepts that we take as given in classical go.

solution?

The C4 group has too many liberties to kill, and we cannot win by territory while the D3 goup is alive. So we have to kill the D3 group. I found the following moves:

(before this I’d naturally do the F5, F6 exchange, but you can’t)
Whites best response with the answer:

Then:

In classical go white would throw in at G2, but she cannot do it here, so she is dead.

[antonTobi]

You got it, well done!

Problem 8

Demo board

[martin3141]

Spoiler

I believe the answer is B3 for Black. If White blocks with C3, Black can first atari with B1, White A2 is forced, then C2 captures.

Another Variation is Black B3, White C2. Black keeps separating White with C3, and eventually White runs into Blacks E2 stone.

Note that black must not start with the B1 Atari because this reduces the liberties of the C1-D1 chain, thus making Whites extention at C2 effective as a response to B3.

[antonTobi]

Completely correct!

The next one is quite difficult…

Problem 9

Demo board

[antonTobi]

Since this problem is very hard, I’ll provide some hints below, in the form of two incorrect first moves and their refutations.

Failure 1

White wins by one move.

Failure 2

D3 and E2 are miai; white wins by one move.

[belabacsijolvan]

next move

Is it C2? It seems to work. If it doesn’t, can you please tell me the next move of whites refutation?

[antonTobi]

A good attempt, but it doesn’t quite work!

Refutation

[belabacsijolvan]

solution?

From the three wrong attempts I think we need to put pressure onto the D1 stone. (also there is not many moves left )
D2 seems to lead to this:

or something like this:

(this is essentially Failure 2, but with playing D2 in sente beforehand)
Black wins both of those. Is D2 right?

[Groin]

I was just considering D2 and D4 combo too
I don’t really see other choice for b

[antonTobi]

Spoiler

I’m not sure about the order of moves that lead to your diagrams, but the first one is actually winning for white!
A4 B5 A3 A5 D5

Even more spoiler

You are very close, D2 is indeed the correct first move, and the second diagram is one possible continuation. You just need to find a different way to play in the first diagram to make it winning for black.